This paper presents a theoretical framework and pilot study that examines the social context of the mental health treatment system and its impact on the spread of HIV among people with serious mental disorders. Recent epidemiological evidence indicates that mental illness clients may be at especially high risk of contracting HIV/AIDS. Mental health professionals' efforts to respond to the emerging epidemic, however, have been limited and focused primarily on individual-level interventions to change risk behavior. Virtually no consideration has been given to how treatment environments influence client risk behavior and/or the effectiveness of HIV prevention efforts. The perspective outlined in this paper builds on existing clinical research and proposes a general sociological framework for researching mental illness clients' HIV risk that emphasizes the clinical sexual culture of treatment programs. In an effort to develop preliminary measures and test key assumptions of the proposed framework, a small pilot study was conducted at a large state psychiatric hospital in the Midwest. The results suggest that clinical sexual culture does have a significant impact on the way both the patients and staff think about the management of patient sexual expression and HIV/AIDS at the hospital. More generally, the findings provide preliminary support for the theoretical framework presented.