An understanding of men's motivations to avoid risk behavior is needed to create efficacious HIV prevention programs for HIV-positive men who have sex with men (MSM). This study investigates the relationship between sexual risk behavior and HIV prevention altruism, which is defined as the values, motivations, and practices of caretaking towards one's sexual partners to prevent the transmission of HIV. In a sample of 637 HIV-positive MSM, HIV prevention altruism significantly protects against serodiscordant unprotected anal intercourse (SDUAI) in crude analysis, but not after adjustment for drug use and compulsive sexual behavior. HIV prevention altruism is also related to not engaging in anal intercourse, but is not related to serodisclosure to secondary partners. Lack of altruism appears related to sexual risk behavior in HIV-positive MSM, although other psychological and contextual factors play significant roles. The promotion of HIV prevention altruism may provide a formidable new direction for HIV prevention programs.