SisterLove Inc., a community-based organization (CBO) in Atlanta, Georgia, evaluated the efficacy of its highly interactive, single-session HIV prevention intervention for black women, the Healthy Love Workshop (HLW). HLW is delivered to pre-existing groups of women (e.g., friends, sororities) in settings of their choosing. Eligible groups of women were randomly assigned to receive the intervention (15 groups; 161 women) or a comparison workshop (15 groups; 152 women). Behavioral assessments were conducted at baseline and at 3- and 6-month follow-ups. Among sexually active women at the 3-month follow-up, HLW participants were more likely than comparison participants to report having used condoms during vaginal sex with any male partner or with a primary male partner, and to have used condoms at last vaginal, anal or oral sex with any male partner. At the 6-month follow-up, HLW participants were more likely to report condom use at last vaginal, anal or oral sex with any male partner, and having an HIV test and receiving their test results. The study findings suggest that a single-session intervention delivered to pre-existing groups of black women is an efficacious approach to HIV prevention. This study also demonstrates that a CBO can develop and deliver a culturally appropriate, effective HIV prevention intervention for the population it serves and, with adequate resources and technical assistance, rigorously evaluate its intervention.