OBJECTIVE The purpose of this study was to describe human immunodeficiency virus (HIV)-associated risk behaviors among adolescents attending a clinic for the treatment of sexually transmitted disease in New York City. METHODS A total of 4,585 volunteers were interviewed and HIV-tested, including 456 adolescents (aged 13-19 years), of whom 220 were women (48%) and 236 men (52%). RESULTS Fewer than 1% of the 456 adolescents said they injected drugs. Unprotected vaginal sex was the most common sexual behavior, with 93% of adolescents reporting "always" having vaginal sex, and 57% "rarely or never" using condoms. Anal sex was reported by 18%. Twenty percent of adolescent men had paid for sex, compared to just 1% of women, whereas 3% of men and 4% of women had traded sex for money or drugs. Nine women and three men tested HIV seropositive. All three HIV-positive men reported having had receptive anal sex with men. Among women, HIV seropositivity was most strongly associated with crack cocaine use and trading sex for money or drugs. CONCLUSIONS HIV prevalence was high, with most infections owing to sexual transmission rather than intravenous drugs. The increased risk of HIV infection in adolescent women was associated with high-risk sex related to crack use and the exchange of sex for money or drugs.