Study findings showed that older youth were less likely to report having prosocial peers and more likely to report having antisocial peers; and they were more likely to engage in behaviors that put them at risk for HIV infection. Also, being homeless a longer time predicted fewer prosocial peers, more antisocial peers, and more HIV-risk peers. Heterosexual youth reported fewer HIV-risk peers and more prosocial peers. Youth recruited from agencies were more likely to report having prosocial peers; and having prosocial peers predicted less sexual behavior that put them at risk for HIV and less antisocial behavior. Having HIV-risk peers predicted all problem behaviors measured. Once the association between antisocial and HIV-risk peers was accounted for independently, having antisocial peers did not independently predict sex-risk or drug-risk behaviors. Based on these findings, the authors recommend the development of interventions that promote the influence of prosocial peers and diminish the influence of HIV-risk peers on HIV risk-taking behaviors, so as to help prevent the further spread of HIV among homeless youth. For this study, homeless youth were selected in Los Angeles County through a three-step process of sampling, screening for eligibility and recruitment, and assessment. A “homeless” youth was defined as ranging in age from 12 to 20 years old and having spent at least 2 consecutive nights away from home either without their guardian’s permission or after having been told to leave home. An audit was conducted among all sites serving homeless youth, including shelters, community-based drop-in centers, and street hang-out sites over 3 weeks. The final sample consisted of 696 youth (slightly over 50 percent male). The variables measured pertained to demographics, engagement with street life, peer characteristics, and problem behaviors (antisocial behavior, HIV sexually risky behaviors, and drug-using behaviors risky for HIV). 2 tables, 2 figures, and 36 references