We report on the prevalence of human immunodeficiency virus (HIV) infection among psychiatric patients in a New York City shelter for homeless men. We reviewed the records of all 90 men discharged from the shelter psychiatry program to community housing over a 2-year period. HIV serostatus was recorded for 62 of the 90 men. Of these 62, 12 (19.4%) were positive. There were 28 men whose serostatus was not recorded. Data on the HIV risk behaviors of these 28 men suggested that seroprevalence could have been similarly high among them. The results indicate an urgent need to develop and apply preventive interventions for HIV in this population.