CONTEXT: High-risk sexual behavior is increasingly prevalent among men who have sex with men (MSM) and among men with a history of repeat testing for HIV. OBJECTIVES: The study assessed whether one counseling intervention session focusing on self-justifications (thoughts, attitudes, or beliefs that allow the participant to engage in high-risk sexual behaviors) at most recent unprotected anal intercourse (UAI) is effective in reducing future high-risk behaviors among HIV-negative men. DESIGN, SETTING, AND PARTICIPANTS: A randomized, controlled, counseling intervention trial was conducted at an anonymous testing site in San Francisco, California, between May 1997 and January 2000. Participants were 248 MSM with a history of at least one previous negative HIV test result and self-reported UAI (receptive or insertive) in the previous 12 months with partners of unknown or discordant HIV status. Two intervention groups received standard HIV test counseling plus a cognitive-behavioral intervention, and two control groups received only standard HIV test counseling. Follow-up evaluation was at 6 and 12 months. MAIN OUTCOME MEASURE: Number of episodes of UAI with nonprimary partners (of unknown or discordant HIV status) in the 90 days preceding the interview was measured via self-report during face-to-face interview. RESULTS: A novel counseling intervention focusing on self-justifications significantly decreased the proportion of participants reporting UAI with nonprimary partners of unknown or discordant HIV status at 6 and 12 months (from 66% to 21% at 6 months and to 26% at 12 months, p =.002; p <.001) as compared with a control group when added to standard client-centered HIV counseling and testing. CONCLUSIONS: A specific, single-session counseling intervention focusing on a reevaluation of a person's self-justifications operant during a recent occasion of high-risk behavior may prove useful in decreasing individual risk behavior and thus limiting community-level HIV transmission.