Previous research has found high levels of HIV seroprevalence and risk behavior among people with severe mental illness living in the community. Risk in this population is associated with high prevalence of unprotected sex with multiple, casual, or high-risk sexual partners; high levels of sexual contact between men with severe mental illness and other men; use of injection drugs or sexual contact within injection drug user (IDU) social networks; elevated rates of alcohol and noninjected drug use, especially the use of crack cocaine and the exchange of sex for drugs; and patterns of “survival sex” to obtain food, money, or a place to stay. A number of theoretical models have been developed to guide HIV risk behavior change interventions. This paper describes the theoretical underpinnings of skills-based HIV risk reduction interventions, and the elements critical to successful HIV risk behavior change as delineated by this model. We then discuss how these elements were operationalized in an HIV prevention intervention successfully implemented in urban community mental health clinics serving people with mental illness. Effective, theory-driven HIV prevention interventions can be successfully incorporated into the daily service life of community-based mental health clinics.