• Two structured interviews, the Schedule for Affective Disorders and Schizophrenia—Lifetime (SADS-L) and the National Institute of Mental Health Diagnostic Interview Schedule (NIMH-DIS), were compared as methods of reducing information variance in the diagnostic process. Forty-two patients newly admitted to an alcohol treatment unit were randomly selected and were independently interviewed using the SADS-L and NIMH-DIS. The order of the interviews was random and they were separated by three to four days. Interrater reliability for each interview schedule was calculated using the k statistic and was found to be high. The degree of diagnostic concordance between the two interview schedules for several diagnostic categories was also found to be high.