Objective: To determine the prevalence of human immunodeficiency virus (HIV) infection among the homeless of Denver and to describe behaviors in the homeless that may be associated with HIV infection, Design: A cross-sectional cohort study, Methods: From July 1990 through June 1994, the authors conducted an unlinked survey collecting demographic and risk exposure data, and from August 1990 through June 1992, a more detailed risk behavior survey was completed on persons who attended the largest homeless clinic in Denver. Results: For the combined survey years, the overall seroprevalence rate in the unlinked survey was 0.9%. Men were more likely to be seropositive than women (1.3% versus 0.1%) (P < 0.001). Black and Hispanic men had higher seroprevalence rates than white men (3.1% and 2.2% versus 0.5%) (P < 0.001). Gay and bisexual men, men vr ho were injection drug users, and men with partners at risk had a nearly fivefold higher seroprevalence rate compared to other risk groups (3.1% versus 0.7%, P < 0.001). During the I study Sears, 14 of homeless persons tested positive for tuberculosis. In the risk behavior survey; 41% of the clients reported previous injection drug use (since 1978), and 22% reported recent rise (past 12 months); of this 22%, 16% reported sharing their works (needles and paraphernalia). Seventy percent of the study participants stated that they. changed their sexual behavior, and 39% reported using condoms in the past 12 months. Conclusions: In this homeless Denver population, there is a low seroprevalence of HIV but a high rate of HIV risk behavior Certain groups of homeless persons are at high risk for HIV infection, targeted interventions are necessary.