The objective of this study was to assess and compare the prevalence of high-risk sexual behaviors among young HIV-negative (n=8064) and HIV-positive (n=171) men who have sex with men (MSM) on predictors of unprotected anal intercourse (UAI). Using venue-based time-space sampling, 8235 MSM aged 15-25 were anonymously surveyed as a part of the Community Intervention Trial for Youth (CITY). The Project was conducted in 13 communities across the USA from 1999 to 2002. Forty percent of HIV-positive men and 34% of HIV-negative men reported that they had UAI in the previous 3 months. HIV-positive MSM were more likely than their uninfected peers to have traded sex within the previous year, to have had sex while high during their last sexual encounter, and to have UAI with a greater number of partners. Multivariate analyses indicated that for HIV-negative men, positive peer norms regarding safer sex and being Black or Latino predicted avoidance of UAI. Among HIV-positive men, having social support for safer sex and positive peer norms predicted avoidance of UAI. Young HIV-positive MSM are a relevant subgroup for prevention because they constitute a significant source from which future infections could be generated.