Since the outbreak of the AIDS epidemic, gay men have made impressive changes in their sexual behavior. Notwithstanding these changes, there are several studies that show considerable within-subject variability in risk categories, indicating that for a substantial number of gay men it is difficult to be consistently safe. A large number of studies have examined the relationship between sexual behavior and determinants of that behavior. This review reports and discusses the findings with regard to demographic, situational, behavioral, and psychosocial determinants.