Women in substance abuse treatment often have co-occurring mental health disorders and a history of trauma; they are also at high risk for HIV infection and other sexually transmitted diseases via unprotected sex. A quasi-experimental study evaluated the effectiveness of trauma-enhanced substance abuse treatment combined with HIV/AIDS prevention (N = 122) on reducing sexual risk behaviors compared to treatment with services-as-usual (N = 110). Participants in the services-as-usual condition were 2.8 times more likely to engage in unprotected sex at the 6-month follow-up and 4.5 times more likely to do so at the 12-month follow-up than those in the intervention program. (Contains 3 tables and 1 figure.)