AIDS Education and Prevention 23(1): 1-12 Black men who have sex with men (BMSM) are disproportionately affected by the HIV epidemic, yet few prevention interventions have been developed specifically for them. Recent studies suggest that the Internet is a promising intervention delivery avenue. We describe results from our formative work in developing a theory-based online HIV/STI prevention intervention for young BMSM including focus groups, semistructured interviews, and usability testing. The Intervention, HealthMpowerment.org, was created based on the Institute of Medicine’s integrated model of behavior change with extensive input from young BMSM. Key interactive Web site features include live chats, quizzes, personalized health and hook-up/sex journals, and decision support tools for assessing risk behaviors. Creating an interactive HIV/sexually transmitted infection web site for BMSM was a complex process requiring many adjustments based on iterative feedback throughout all development stages. Preliminary satisfaction, content acceptability, and usability findings support the use of the Internet to deliver risk reduction messages to young BMSM.