Selected findings from the Multicenter AIDS Cohort Study (MACS) of homosexual/bisexual men are reviewed. High risk sexual behaviors, the use of drugs/alcohol, condom use, and behavior change are addressed in a public health context. The potential significance of education/behavior modification programs as strategies for public health intervention emerges from these findings. Until there is a realistic timetable for vaccine availability and more effective chemotherapy, the MACS provides the opportunity to continue to study the effects of behavior change on the AIDS epidemic.