Most of the people have had multiple psychiatric admissions and courses of psychotropic medications. In addition, most are unemployed and rely on social welfare benefits. They typically do not fit into existing health care and substance abuse treatment programs, they receive inferior medical care and have high morbidity and mortality, and they are not welcome in traditional treatment programs. Specific studies are cited on the emergence of the AIDS epidemic in the psychiatric population, the prevalence of HIV infection among adults with severe mental illnesses, rates of HIV infection among psychiatric patients and other groups in New York City, the detection of HIV infection in psychiatric settings, the social context of HIV infection among those with severe mental illnesses, the relationship between psychiatric disorders and HIV risk, the prevalence of substance abuse among people with serious psychiatric disorders, and the interaction between substance use and sexual risk behaviors in the psychiatric population. Future research needs on the risk and prevalence of HIV infection among persons with severe mental illnesses are noted. 47 references and 2 tables