Postservice Mortality in Vietnam Veterans: 30-Year Follow-up

Background  During the 1980s, the postservice mortality component of the Vietnam Experience Study was conducted to examine the health effects of the Vietnam experience. This study was limited by the relatively short follow-up and the young age of the veterans. Thus, a follow-up mortality investigation on this cohort was undertaken to further assess the impact of the Vietnam experience on chronic conditions.

Methods  Vital status and underlying cause-of-death data on the Vietnam Experience Study cohort (18 313 male US Army veterans) were retrospectively ascertained from the end of the original study through 2000. Cox proportional hazards regression was used to calculate crude and adjusted rate ratios (RRs) for all-cause and cause-specific mortality, comparing Vietnam and non-Vietnam veterans.

Results  All-cause mortality was 7% higher in Vietnam vs non-Vietnam veterans during 30-year follow-up (95% confidence interval [CI], 0.97-1.18). The excess mortality among Vietnam veterans was isolated to the first 5 years after discharge from active duty and resulted from an increase in external causes of death (RR, 1.62; 95% CI, 1.16-2.26). Cause-specific analyses revealed no difference in disease-related mortality. Vietnam veterans, however, experienced excess unintentional poisoning (RR, 2.26; 95% CI, 1.12-4.57) and drug-related (RR, 1.70; 95% CI, 1.01-2.86) deaths throughout follow-up.

Conclusions  Vietnam veterans continued to experience higher mortality than non-Vietnam veterans from unintentional poisonings and drug-related causes. Death rates from disease-related chronic conditions, including cancers and circulatory system diseases, did not differ between Vietnam veterans and their peers, despite the increasing age of the cohort (mean age, 53 years) and the longer follow-up (average, 30 years).

During the 1980s, the Centers for Disease Control and Prevention conducted the Vietnam Experience Study (VES) to examine the long-term health effects of military service in Vietnam through (1) an assessment of postservice mortality, (2) a detailed health interview, and (3) a comprehensive medical, psychological, and laboratory evaluation. Reports from the VES have been published,^1-3 including findings from the postservice mortality component.^4,5 The Vietnam experience included a wide array of possible health-influencing factors, such as exposure to psychological stressors associated with war and combat, infectious diseases prevalent in Vietnam, pesticides and herbicides, and misuse of drugs and alcohol.⁵

The original VES postservice mortality investigation⁴ followed 18 313 US Army veterans from their date of discharge from active duty (1965-1977) through December 31, 1983. During the first 5 years after discharge, Vietnam veterans experienced excess all-cause mortality, primarily from external causes (ie, motor vehicle collisions, unintentional poisonings, suicides, and homicides), compared with veterans who served during the same period but not in Vietnam. In addition, drug-related deaths were higher among Vietnam veterans throughout follow-up. Deaths from diseases of the circulatory system were lower among Vietnam veterans than among non-Vietnam veterans.

The original mortality study followed participants for an average of 13.5 years and was somewhat limited by the young age of the cohort (mean age, 36.1 years) and the relatively small number of deaths (n = 446). Thus, a follow-up mortality investigation on the same cohort of Vietnam-era veterans was undertaken to further assess the impact of the Vietnam experience on cause-specific mortality, especially chronic conditions such as cancer. An estimated 8.4 million Vietnam-era veterans live in the United States, and veterans constitute nearly 40% of all US men aged 50 to 59 years.⁶ Strong concern remains, in the media and among veterans themselves, regarding the health effects of service in Vietnam, or "in-country effects."⁷ Several studies have linked exposure to herbicides (ie, Agent Orange) with cancers such as non-Hodgkin lymphoma,⁸ Hodgkin disease,⁸ soft tissue sarcoma,⁸ and, most recently, chronic lymphocytic leukemia,⁹ as well as with diabetes mellitus.¹⁰ The findings from this follow-up mortality investigation add to the knowledge of long-term health effects associated with Vietnam service.

The study population comprised men who served in the US Army during the Vietnam era and whose service records were received by the National Personnel Records Center between September 1, 1964, and June 30, 1977. The original cohort was identified through a random sample of 48 513 service records selected from the nearly 5 million records on file at the National Personnel Records Center (Figure 1). Of these, 18 581 veterans met the following criteria for study eligibility, which were chosen to increase comparability between men who served in Vietnam and men who served elsewhere: (1) entered military service for the first time between 1965 and 1971, (2) served only 1 term of enlistment, (3) had at least 16 weeks of active service time, (4) earned a military occupational specialty other than "trainee" or "duty soldier," and (5) had a pay grade no higher than E5 on discharge from active duty. Qualified participants were classified as Vietnam veterans if they served at least 1 tour of duty in Vietnam or as non-Vietnam veterans if they never served in Vietnam and served at least 1 tour of duty in the United States, Germany, or Korea. Veterans who died while on active duty were excluded from the study (234 Vietnam and 34 non-Vietnam veterans). The final sample comprised 9324 Vietnam and 8989 non-Vietnam veterans. Further details regarding participant selection, sample size, and power have been published previously.^4,5

The original mortality study retrospectively ascertained vital status from the veterans' date of discharge from active duty through December 31, 1983, and identified 446 deceased veterans (246 Vietnam and 200 non-Vietnam veterans). The present study extended follow-up through December 31, 2000, an additional 17 years. We ascertained vital status using 3 national mortality databases: the Department of Veterans Affairs Beneficiary Identification Record Locator Subsystem (VA BIRLS) death file, the Social Security Administration Death Master File (SSA DMF), and the National Death Index Plus (NDI Plus). The VES database contained the following personal identifiers: Social Security number, military identification number, first and last name, date of birth, and state of birth. Each mortality database used different matching criteria. For example, the VA BIRLS search used exact social security number matching only, whereas the SSA DMF and NDI Plus searches used various algorithms of social security number, name, and birth date to identify potential matches.

We manually reviewed the potential matches from each data source separately, taking into consideration digit transposition errors in social security numbers and birth dates and possible name changes and misspellings, and classified the matches as "true," "false," or "questionable." The final determination of vital status was obtained by combining information from all 3 mortality data sources. As needed, we requested additional information, such as death certificates and dates of enlistment and separation, to confirm vital status of questionable matches. Veterans who had a true match in at least 1 of the 3 national databases were determined to be deceased. All veterans whose vital status was uncertain because of a lack of data to resolve questionable matches or who were not identified by any of the national death databases were assumed to be living as of December 31, 2000.

Underlying cause-of-death codes were obtained from the NDI Plus, the only national mortality database with cause-of-death information, for deaths that occurred between January 1, 1984, and December 31, 2000. Cause of death was coded according to the International Classification of Diseases (ICD) revision in place at the time of death: the Ninth Revision (ICD-9)¹¹ for deaths between January 1, 1979, and December 31, 1998, and the Tenth Revision (ICD-10)¹² for deaths between January 1, 1999, and December 31, 2000. In cases in which cause-of-death codes were not available from the NDI Plus, we attempted to obtain official copies of death certificates, which were coded by an experienced nosologist at the Centers for Disease Control and Prevention's National Center for Health Statistics (NCHS). The NCHS provided a crosswalk that enabled us to convert ICD-9 and ICD-10 deaths into the NCHS list of 113 selected causes of death, plus separate classifications for alcohol-, drug-, and firearm-related deaths.¹³ For comparison with the original study, we then categorized the 113 selected causes into the 15 ICD-9 chapter headings, grouped by major organ system. We provided specific ICD-9 codes for external causes, neoplasms, and circulatory system diseases because these had been previously identified as areas of interest.

Crude death rates were calculated separately for Vietnam and non-Vietnam veterans based on person-years at risk. Person-years at risk began the day the veteran was discharged from active duty and ended on the date of death or December 31, 2000, whichever was sooner. We calculated crude rate ratios (RRs) of Vietnam to non-Vietnam veterans and corresponding 95% confidence intervals (CIs). Because of variability in the crude RRs in the earlier study, we present results separately for 2 intervals (0-5 years and >5 years). For descriptive purposes, we also calculated death rates and crude RRs in the later follow-up period by 10-year intervals (>5-15, >15-25, and >25 years). All crude and adjusted RRs were calculated using the PHREG procedure in SAS (SAS System for Windows, release 8.2; SAS Institute Inc, Cary, NC).

We used Cox proportional hazards regression¹⁴ to calculate adjusted RRs for all-cause mortality, using the model from the original VES postservice mortality investigation as a starting point. The original model was stratified on primary military occupational specialty (tactical vs nontactical) and enlistment status (volunteer vs draftee) and was controlled for race (white vs nonwhite), age at discharge from active duty (in years), Army General Technical Test score (in units), pay grade at discharge (E1-E3 vs E4-E5), and year of discharge (before 1970 vs 1970 or later).^4,5 The Army General Technical Test score measures general aptitude taken at entry into the military.⁵ For each variable in the model, we evaluated the proportional hazards assumption (that the RR is constant over time), assessed confounding, and tested for effect modification.^15,16 We also assessed the linearity assumption for covariates treated as continuous.¹⁶

For the first interval (0-5 years), the model was identical to that used in the original VES postservice mortality investigation. In the greater-than-5-years period, the proportional hazards assumption seemed to fail for pay grade at discharge from active duty, and the association of mortality with age at entry seemed to be nonlinear. Therefore, we modeled pay grade as having a different RR for each of 3 intervals (>5-15, >15-25, and >25 years) and categorized age into 3 groups (<21, 21-25, and ≥26 years). We developed and assessed Cox regression models for major ICD-9 chapters with 50 or more total deaths using strategies similar to those described previously herein for all-cause mortality.

Standardized mortality ratios (SMRs) and 95% CIs were used to compare veteran death rates with those of the US male population, adjusted for age, race, and calendar year. These analyses were limited to deaths through 1998 because US rates that incorporate ICD-10 were not available at the time. We used the Life Table 1 Analysis System software developed by the Centers for Disease Control and Prevention's National Institute for Occupational Safety and Health.^17,18

We identified 1138 new deaths during the follow-up investigation, 5 of which occurred before 1984 but were not previously identified. In this follow-up study, 98% of the new deaths were identified by the NDI Plus, 95% by the SSA DMF, and 70% by the VA BIRLS. In addition, 67% of the deaths were confirmed by all 3 sources, 29% by 2 sources, and 4% by 1 source. As of December 31, 2000, 1584 deceased veterans (838 Vietnam and 746 non-Vietnam veterans) were identified in the VES cohort, including the 446 deaths reported in the original study. Vietnam veterans accumulated 278 263 person-years at risk, and non-Vietnam veterans accumulated 267 001 person-years, with average follow-up of 29.8 years.

As reported in the original VES postservice mortality investigation, some differences in the demographic and military service characteristics were observed between Vietnam and non-Vietnam veterans (Table 1).⁴ The groups were similar in demographic characteristics such as race and age at entry; however, Vietnam veterans entered the military earlier and were more likely to have military training in tactical operations, to serve in an infantry unit, to receive an honorable discharge, and to be discharged at a higher pay grade.

All-cause mortality was 7% higher in Vietnam veterans than in non-Vietnam veterans during the entire follow-up period; however, this difference was not statistically significant (Table 2). As found in the original mortality study, Vietnam veterans experienced statistically significantly higher mortality than non-Vietnam veterans during the first 5 years after discharge from active duty. No statistically significant difference in all-cause mortality was observed between Vietnam and non-Vietnam veterans throughout the remaining follow-up period.

We excluded 201 veterans (1.1%) from the adjusted all-cause mortality analysis because of missing values for race and Army General Technical Test score. After adjustment for entry and military service characteristics, the RR for all-cause mortality among Vietnam veterans was 1.59 (95% CI, 1.17-2.16) during the first 5 years after discharge and 1.08 (95% CI, 0.97-1.20) during the remaining years of follow-up.

We obtained underlying cause-of-death codes for 1119 (98.3%) of the 1138 newly identified deaths plus 1 of the original 9 VES deaths with missing cause of death. All but 4 cause-of-death codes were obtained from the NDI Plus (a nosologist at the NCHS provided cause-of-death codes for 3 death certificates and 1 report of death of a US citizen abroad). We could not obtain cause-of-death codes for 16 Vietnam and 11 non-Vietnam veterans (ie, data were missing from the original study, were not released by states, or were unavailable for some deaths identified by the SSA DMF or the VA BIRLS); thus, we excluded these deaths from the cause-specific analyses.

Crude mortality rates did not differ significantly between Vietnam and non-Vietnam veterans for any of the disease-related ICD-9 categories, including neoplasms and diseases of the circulatory system (Table 3). However, external-cause mortality rates were statistically significantly higher among Vietnam veterans throughout the entire follow-up period.

When neoplasm-related deaths were examined by type and primary site, mortality from any specific type of cancer did not differ among Vietnam and non-Vietnam veterans (Table 4). As expected, malignant neoplasms of the trachea, bronchus, and lung were the most frequently reported neoplasm-related deaths in the cohort. In the adjusted model for neoplasms, effect modification was observed between Vietnam status and pay grade at discharge from active duty such that Vietnam veterans discharged at a low pay grade had a higher risk than non-Vietnam veterans of dying of cancer (adjusted RR, 1.64; 95% CI, 0.94-2.89), whereas those discharged at a high pay grade had a lower risk (adjusted RR, 0.82; 95% CI, 0.63-1.07).

Because of the lower risk for circulatory system diseases associated with Vietnam status in the original mortality study, we examined this issue in more detail (Table 5). Most circulatory system disease–related deaths occurred 15 or more years after discharge from active duty, during which time no statistically significant difference was observed in the disease-specific death rates between Vietnam and non-Vietnam veterans. The adjusted model for diseases of the circulatory system also revealed fewer deaths among Vietnam veterans in the first 15 years of follow-up (adjusted RR, 0.56; 95% CI, 0.28-1.15) but not in the remaining years of follow-up (adjusted RR, 1.06; 95% CI, 0.85-1.32). During the later follow-up period, however, circulatory system disease deaths were higher among Vietnam veterans discharged from active duty in 1970 or later (adjusted RR, 1.43; 95% CI, 1.02-1.99) and lower among Vietnam veterans discharged before 1970 (adjusted RR, 0.83; 95% CI, 0.62-1.12) than among non-Vietnam veterans.

The excess number of deaths from all external causes seems to be isolated to the first 5 years after discharge from active duty (Table 6). In the early postdischarge period, the crude RR for motor vehicle collision–related deaths was statistically significantly elevated. The crude RRs for suicides and homicides also were somewhat elevated in the first 5 years but not in the remaining years of follow-up. Deaths from unintentional poisonings were statistically significantly higher among Vietnam veterans in the later follow-up period (Table 6) and during the entire follow-up period (RR, 2.26; 95% CI, 1.12-4.57). Adjustment for entry and military characteristics increased the RR slightly for external causes of death in both periods (adjusted RR, 1.76; 95% CI, 1.25-2.49 for 0-5 years; adjusted RR, 1.19; 95% CI, 0.99-1.45 for >5 years).

Using NCHS definitions, all external and disease-related deaths were categorized to indicate whether they were alcohol-, drug-, or firearm-related (Table 7). This classification revealed an elevated but nonsignificant RR for firearm-related deaths in the first 5 years after discharge from active duty among Vietnam veterans. Drug-related deaths were more common among Vietnam veterans than non-Vietnam veterans during the entire follow-up period (RR, 1.70; 95% CI, 1.01-2.86).

The observed death rates for Vietnam and non-Vietnam veterans were statistically significantly lower than the expected US death rates for men through 1998 (Table 8). Among Vietnam veterans, however, all-cause mortality was slightly higher than expected during the first 5 years after discharge from active duty. This pattern may be explained partly by a relatively high SMR for motor vehicle accidents, accidental poisonings, and other accidents combined among Vietnam veterans (SMR, 1.33; 95% CI, 1.04-1.71) and a low SMR among non-Vietnam veterans (SMR, 0.82; 95% CI, 0.60-1.14) in the early postdischarge period. The death rate from malignant neoplasms was lower than that in the US population for Vietnam (SMR, 0.76; 95% CI, 0.62-0.94) and non-Vietnam (SMR, 0.93; 95% CI, 0.76-1.12) veterans.

Epidemiologic studies of the VES cohort offer an excellent opportunity to better understand the health implications of the Vietnam War. Assessment of postservice mortality is one way to address the concerns of in-country effects that Vietnam veterans have raised.⁷ This mortality study is unique because it has average follow-up of nearly 30 years and a mean cohort age of 53 years (range, 46-67 years) at the end of the study. Because of the longer follow-up, we could examine cause-specific mortality of chronic diseases with long latency periods, which previous studies have not adequately addressed.

As in the original mortality study, we observed no difference in all-cause mortality after the first 5 years after discharge from active duty. In the initial mortality study, three fourths of all deaths resulted from external causes. In this follow-up investigation, external causes, diseases of the circulatory system, and neoplasms each accounted for a substantial proportion of overall deaths (38.5%, 23.1%, and 17.5%, respectively), as would be expected based on the leading causes of death for US men in the same age range.¹⁹ We found no difference in disease-related mortality in Vietnam and non-Vietnam veterans during the entire follow-up period.

The decrease in the number of deaths from diseases of the circulatory system observed among Vietnam veterans in the original VES mortality study was no longer evident during the extended follow-up period. There was a possible excess in deaths from circulatory system diseases among a specific subgroup of Vietnam veterans (those discharged from active duty in 1970 or later) after the first 15 years after discharge. The biological plausibility of this finding, however, is unclear and may merit further investigation.

The death rates for all cancer and site-specific cancers, including Hodgkin disease, non-Hodgkin lymphoma, and leukemia, did not differ between Vietnam and non-Vietnam veterans, although 95% CIs were wide for some site-specific neoplasms. The average follow-up of 30 years should be sufficient to capture a potentially long latency period for many cancers, if the exposure occurred during military service. Evidence links occupational herbicide exposure to site-specific cancers^8,9; however, because the VES cohort was selected on the basis of time and place of service, rather than on Agent Orange exposure, we could not examine the relation between herbicide exposure and cancer mortality.

As reported previously,^4,5 the rate of death from external causes was higher among Vietnam vs non-Vietnam veterans in the first 5 years after discharge from active duty. After the first 5 years of follow-up, no difference occurred in deaths from external causes overall; however, the rate of death from unintentional poisonings was higher among Vietnam veterans during this period. We also found an excess of drug-related deaths among Vietnam veterans during the entire follow-up period. These findings corroborate those of previous research linking combat exposure with elevated illicit drug use²⁰ and posttraumatic stress disorder with traumatic deaths, including unintentional poisonings.²¹

The extent of overlap between the definitions of unintentional poisonings and drug-related deaths is noteworthy. The external cause-of-death subcategory labeled as "accidental poisonings and exposure to noxious substances" includes deaths caused by exposure to drugs, alcohol, organic solvents, hydrocarbons, other gases and vapors, pesticides, and other chemicals. In this study, 31 of the 37 unintentional poisonings were drug related. The category of "drug-related deaths" is larger (n = 61) and includes the 31 drug-related unintentional poisonings plus 14 mental and behavioral disorders (ie, drug dependence or nondependent abuse), 8 suicides, and 8 deaths of undetermined intent. Although Vietnam veterans were more likely to die of drug-related causes, the contribution to the overall number of deaths was relatively small.

Our findings that veterans have lower mortality rates than the US population support the concept of the "healthy veteran effect," an extension of the "healthy worker effect," that has been observed in other studies comparing veterans to the general population.²² In general, military personnel are healthier than the general population because of military selection criteria emphasizing health and physical fitness. This study provides evidence that the healthy veteran effect diminished somewhat during the extended follow-up, that is, the difference between the observed and expected number of deaths decreased as the cohort aged.

The results of this study can be compared with those of 2 similarly designed cohort studies that examined the relation between the Vietnam experience and subsequent mortality. The Australian Vietnam veteran study assessed the postservice mortality of 19 205 Vietnam veterans and 25 677 non-Vietnam veterans through 1981.^23,24 This study found that the death rate for Vietnam veterans was 1.3 times that for non-Vietnam veterans; however, the excess deaths were limited to Engineer Corps members (RR, 2.5). Cause-specific analyses showed elevated mortality from diseases of the circulatory system and external causes of death. The findings of this mortality study were not examined by time since discharge from active duty, and no follow-up on the Australian Vietnam cohort has been published, to our knowledge.

More recently, the VA Marine Corps Vietnam veteran study followed 22 062 veterans from discharge from active duty through 1991.²² Similar to the VES, the VA Marine Corps study found an excess of all-cause mortality among Vietnam veterans (RR, 1.14), with a higher RR reported in the first 5 years of follow-up (RR, 1.26). No other statistically significant findings were reported; however, elevated RRs were observed for deaths from external causes, infectious diseases, larynx cancer, and all cancers among those followed for 16 years or more.

In addition, 2 mortality studies have assessed the health impact of herbicide exposure among Vietnam-era veterans. Among "Operation Ranch Hand" Air Force veterans exposed to Agent Orange in Vietnam, rates of death from all causes, neoplasms, and circulatory system diseases did not differ from rates for Vietnam veterans without herbicide exposure; however, exposed veterans experienced excess deaths from external causes in the first 5 years of follow-up.^25,26 Similarly, the mortality experience of Army Chemical Corps veterans did not differ from that of the US male population, except that veterans experienced higher mortality from motor vehicle collisions.²⁷ Both studies found more deaths from digestive system diseases, particularly cirrhosis of the liver, among veterans exposed to Agent Orange; however, this finding was attributable to long-term alcohol use, not herbicide exposure.^25,27 Although the findings of these 2 Agent Orange studies seem to corroborate our results, it is important to reiterate that our investigation examined in-country effects, not herbicide exposure.

This study has several strengths and limitations. Use of multiple sources of vital status ascertainment allowed for a more complete and accurate account of postservice mortality. The NDI Plus is considered the gold standard for identifying deaths in the United States.²⁸ The SSA DMF and VA BIRLS databases also are accurate and reliable sources of mortality information, and all 3 databases have a high degree of sensitivity.^28,29 Thus, we probably identified nearly all deaths in the United States; however, we may have missed some deaths that occurred elsewhere because we did not attempt to verify the vital status of veterans assumed to be living at the end of the study. Two additional reasons for underreporting mortality are that death certificate fields often are incomplete for transient persons, and the database matching criteria depend largely on the accuracy of the social security number. Underreporting is likely to have occurred equally among Vietnam and non-Vietnam veterans; thus, the results of this study should not be substantially biased.

Death certificates are the most common source of underlying cause-of-death data in epidemiologic research and are the basis for national mortality statistics; however, they are not without error.^30,31 Underlying cause of death, as reported on the death certificate, is known to underreport alcohol- and drug-related deaths and to overreport circulatory conditions, ill-defined conditions, and respiratory conditions.^31-34 Neoplasms, in general, are the most accurately diagnosed condition on the death certificate when compared with autopsy results³¹; however, accuracy varies by the primary site of the tumor.³⁵ To the extent that misclassification of the underlying cause of death is similar for Vietnam and non-Vietnam veterans and for the US population as a whole, the RRs and SMRs in this study are unlikely to be biased.

Although death certificates were the single source of cause-of-death data in the original and follow-up studies, the method differed for obtaining cause-of-death codes. In the original VES, death certificates were obtained for all deceased veterans, and underlying cause of death was coded by 2 expert nosologists at the NCHS. For the follow-up study, the NDI Plus, a service introduced after the original VES, provided ICD codes for underlying cause and multiple causes for all US deaths since 1979. Two studies^36,37 have shown that underlying cause-of-death codes obtained from the NDI Plus are comparable to those obtained using standard procedures (ie, 2 trained contractor nosologists reviewing death certificates) and that the NDI Plus is less expensive, is less time-consuming, and requires less effort and staff than conventional methods.

Other strengths of this study are the cohort design and the relatively long follow-up since the Vietnam War. The large number of deaths, compared with the previous examination of this cohort, allows for more detailed analysis of cause-specific mortality, especially for chronic conditions. In addition, the cohort was randomly selected from a national database of US Army veterans, which represents most military personnel stationed in Vietnam. Last, the well-defined cohort was selected to maximize the comparability of Vietnam and non-Vietnam veterans, and we adjusted for residual differences in background characteristics between the groups, thus minimizing the chance that the observed effects resulted from entry or military service characteristics. However, the results of this study apply only to enlisted men with a pay grade of E1-E5 at discharge from active duty, not higher-level enlisted personnel or officers.

The primary findings of this mortality study can be summarized as follows: (1) no excess in all-cause mortality occurred after the first 5 years after discharge from active duty, (2) no excess in neoplasm-related or other disease-related mortality occurred during the entire follow-up period, (3) the overall excess of external-cause mortality among Vietnam veterans was primarily isolated to the first 5 years after discharge, and (4) rates of unintentional poisoning and drug-induced deaths were elevated among Vietnam veterans throughout follow-up. As of December 31, 2000, approximately 91.4% of the VES cohort was presumed living. After examination of 30 years of follow-up data, we did not see any statistically significant excess in mortality among Vietnam veterans compared with their peers; however, because of the relatively small percentage of deceased veterans, continued monitoring of the VES and other Vietnam cohorts may be warranted.

Correspondence: Drue H. Barrett, PhD, National Center for Environmental Health, Centers for Disease Control and Prevention, 1600 Clifton Rd, Mail Stop E-28, Atlanta, GA 30333 (DBarrett@cdc.gov).

Accepted for publication October 3, 2003.

We thank Teresa Schnorr, PhD, Christine Gersic, Patricia Laber, MS, and Steve Spaeth, BS, from the National Institute for Occupational Safety and Health for providing insight on the study protocol and conduct, data collection, and interpretation of death data; Barbara Bauman from the National Personnel Records Center, Han Kang, DrPH, and Tim Bullman, MS, from the Department of Veterans Affairs, and Robert Bilgrad, MA, MPH, and Michelle Goodier from the NCHS for assisting with data collection; Vickie Boothe, BSEE, from the National Center for Environmental Health for aiding with data collection and interpretation of death data; and Tzesan Lee, PhD, from the National Center for Environmental Health for providing statistical advice.

This study was supported by funding from the National Center for Environmental Health, Atlanta.