Phase 1 oncology trials involve risk and offer a relatively low prospect of benefit to participants. Some claim that participants constitute a vulnerable population requiring special protections. We undertook this study to determine whether phase 1 oncology trial participants have demographic and health status characteristics of a vulnerable population. We reviewed participant demographic and health status data from phase 1 trials sponsored by the Cancer Therapy Evaluation Program at the National Cancer Institute that began between 1991 and 2002 and from 11 previously published studies. Main outcome measures were median age, sex, race/ethnicity, performance status, previous therapy, educational achievement level, and health insurance coverage. Almost 10 000 participants in trials sponsored by the Cancer Therapy Evaluation Program had a median age of 57 years, 90% self-identified as white, 93% had near-normal performance status, 85% had some form of health insurance, and 92% had been previously treated for cancer; 20 000 individuals from published studies had comparable profiles. The demographic and health status characteristics of phase 1 oncology trial participants are not those of a conventional vulnerable population and suggest little reason to assume that, as a group, they have a compromised ability to understand information or to make informed and voluntary decisions.