Prevention campaigns to reduce sexual transmission of human immunodeficiency virus (HIV) typically emphasize the initial adoption of safer sex techniques. We present data from a 5-year prospective study to show that the vast majority of resident gay men in San Francisco have made these initial risk reductions. Rather, relapse from safer sex techniques is now the predominant predominant kind of high-risk sex, accounting for approximately two thirds of all prevalent high-risk sex in the 1988 wave of data collection. Predictors of relapse from safer sex are identified, and these are discussed in terms of their implications for preventing relapse from the exclusive practice of safe sex. In communities that have already manifested widespread behavioral risk reductions and in which HIV infection is highly prevalent, finding ways to prevent relapse of behavioral risk reductions will be the next important challenge in the fight against acquired immune deficiency syndrome.