A growing body of research implicates internalized homophobia--the internalization of society's antihomosexual sentiments by gay and lesbian people--as a factor contributing to HIV-related sexual risk behavior in gay and bisexual men. Although accumulating evidence links internalized homophobia and sexual risk behavior, no study has explored the impact of internalized homophobia on efforts to prevent these behaviors. This paper examines the effect of internalized homophobia on gay and bisexual men's awareness of participation in, and perceptions of programs offered by a community-based HIV prevention organization. In Study 1, 595 gay and bisexual men reported their levels of awareness of and participation in HIV prevention programming offered by one community organization. Internalized homophobia was negatively related to men's awareness of the services offered by the organization. However, among the men who were aware of at least one service, internalized homophobia did not further predict service utilization. Study 2 examined 89 gay and bisexual men who participated for a single session in a group-structured, community-based HIV preventive intervention. Pre- to immediate postintervention change in perceptions of condom use self-efficacy was inversely related to internalized homophobia. Internalized homophobia was also a significant negative predictor of the extent to which participants felt similar to and related well with other members of the group. Together, these findings suggest that internalized homophobia may pose multiple barriers to community-based HIV prevention efforts.