OBJECTIVE: Several recent studies confirm elevated rates of human immunodeficiency virus infection among acute and chronic mentally ill adults in large urban areas. This research sought to characterize risk for HIV infection among adults with chronic mental illness and to examine psychosocial factors predictive of risk. METHODS: Two hundred and twenty-five adults with chronic mental illness who were sexually active in the past year outside of exclusive relationships were individually interviewed in community mental health clinics using a structured HIV risk assessment protocol. RESULTS: More than 50 percent of the study participants were sexually active in the past month, and 25 percent had multiple sexual partners during that period. Fifteen percent of the men had male sexual partners. In more than 75 percent of occasions of sexual intercourse, condoms were not used. When participants were categorized as at either high or lower risk for HIV infection based on their pattern of condom use, psychosocial factors that predicted risk level included measures of participants' self- reported efficacy in using condoms, perceptions of social norms related to safer sex among peers and sexual partners, and expectations about outcomes associated with condom use, as well as participants' level of objectively assessed behavioral skills in negotiation and assertiveness in sexual situations. CONCLUSIONS: Interventions aimed at prevention of HIV and AIDS are urgently needed in settings that provide services to persons with chronic mental illness.