OBJECTIVE Reductions in runaways' sexual risk behaviors were evaluated in response to an intensive program to prevent human immunodeficiency virus (HIV) infection and the acquired immunodeficiency syndrome (AIDS). METHODS In a nonrandomized control trial, sexual risk behaviors among 78 runaways at one residential shelter who received up to 30 HIV/AIDS intervention sessions were compared with 67 runaways at a nonintervention shelter with sexual behaviors assessed at baseline and 3 and 6 months. METHODS Runaways were recruited from the only two publicly funded shelters in New York, NY. METHODS The runaways were aged 11 to 18 years, 64% female, and predominantly black or Hispanic. METHODS The intervention addressed general knowledge about HIV/AIDS, coping skills, access to health care and other resources, and individual barriers to safer sex. METHODS Consistent condom use, a high-risk pattern of sexual behavior, and sexual abstinence over a 3-month time frame were assessed. RESULTS As the number of intervention sessions increased, runaways' reports of consistent condom use increased significantly (at 3 months, unique R2 = .06, P less than .05; at 6 months, unique R2 = .09, P less than .05), and their reports of engaging in a high-risk pattern of sexual behavior decreased significantly (at 3 months, unique R2 = .03, P = .06; at 6 months, unique R2 = .04, P less than .05). Abstinence did not change. CONCLUSIONS The demonstrated effectiveness of the intensive HIV/AIDS program highlights the importance of enlarging the scope of most current HIV/AIDS prevention programs.