The enormous HIV/AIDS disparity among African American women and women in other ethnic groups dictates the need to implement the most effective HIV prevention interventions. This study examined the impact of perceived group support on HIV protective behaviors (i.e., attitudes and behaviors related to condom use, alcohol, and drugs) of African American women participating in an HIV prevention intervention. Participants were 398 heterosexual, unmarried African American women older than 18 years who agreed to participate in Sisters Informing Sisters on Topics about AIDS, a widely used HIV prevention program for African American women. Regression analyses revealed that higher perceived support contributed to (1) higher condom negotiation efficacy, (2) higher condom use efficacy, (3) consistent condom use for sexually active participants, (4) higher perception of drug harmfulness, and (5) drug disapproval at posttest. These effects were found while controlling for pretest measures of condom and drug attitudes and use along with age, partner status, length of relationship, and education. The findings suggest that HIV intervention efforts should attend to ways in which women receive and provide support to one another. (Contains 2 tables.)