BACKGROUND: As many as one in three HIV-positive people continue unprotected sexual practices after learning that they are HIV infected. This article reports the outcomes of a theory-based intervention to reduce risk of HIV transmission for people living with HIV infection. METHODS: Men (n=233) and women (n=99) living with HIV-AIDS were randomly assigned to receive either (1) a five-session group intervention focused on strategies for practicing safer sexual behavior, or (2) a five-session, contact-matched, health-maintenance support group (standard-of-care comparison). Participants were followed for 6 months post-intervention. RESULTS: The intervention to reduce risk of HIV transmission resulted in significantly less unprotected intercourse and greater condom use at follow-up. Transmission-risk behaviors with non-HIV-positive sexual partners and estimated HIV transmission rates over a 1-year horizon were also significantly lower for the behavioral risk-reduction intervention group. CONCLUSIONS: This study is among the first to demonstrate successful HIV-transmission risk reduction resulting from a behavioral intervention tailored for HIV-positive men and women.