OBJECTIVES. It is critical to extend community-level acquired immunodeficiency syndrome (AIDS) prevention efforts beyond education alone and to develop models that better encourage behavioral changes. Gay men in small cities are vulnerable to human immunodeficiency virus (HIV) infection due to continued high rates of risk behavior. This research introduced an intervention that trained popular people to serve as behavioral change endorsers to peers sequentially across three different cities. METHODS. Populationwide surveys were conducted of all men patronizing gay clubs in each city to establish risk behavior base rates. After a small cadre of popular "trendsetters" were identified, they received training in approaches for peer education and then contracted to communicate risk reduction recommendations and endorsements to friends. Surveys were repeated at regular intervals in all cities, with the same intervention introduced in lagged fashion across each community. RESULTS. Intervention consistently produced systematic reductions in the population's high-risk behavior (unprotected anal intercourse) of 15% to 29% from baseline levels, with the same pattern of effects sequentially replicated in all three cities. CONCLUSIONS. This constitutes the first controlled, multiple-city test of an HIV prevention model targeting communities. The results support the utility of norm-changing approaches to reduce HIV risk behavior.