We conducted focus groups with 36 men and women who were receiving treatment for a severe and persistent mental illness (SPMI) to learn more about the social context of their intimate relationships and the psychological antecedents of their sexual decision-making. Qualitative analysis of focus group transcripts indicated that a) sexual activity tended to be unplanned and occurred in social networks where HIV risk may be elevated, b) HIV-related knowledge was superficial and insufficient to guide safer sexual behavior, c) participants' HIV risk perception was often based upon factors unrelated to their sexual behaviors, and d) communication skills for HIV risk reduction were poor. We discuss how qualitative methods yielded insights not readily available through quantitative approaches and offer recommendations for HIV risk assessment and prevention among persons with an SPMI.