We report the outcomes of a randomized clinical trial designed to test the effects of a brief single-session risk reduction counseling session intended for use in resource-poor STI clinics. We hypothesized that brief theory-based risk reduction counseling sessions would reduce unprotected vaginal and anal intercourse and prevent STIs during 12 months of observation. We also examined potential moderators of the intervention effects. We included participant gender as a factor in the analyses because there are differences in STI risks between men and women, especially given the gender dynamics in sexual relationships and that men ultimately control the use of condoms. We also tested alcohol use and use of other drugs as moderators of risk reduction outcomes because they are known cofactors for HIV transmission risk behaviors in South Africa.[ 20][ 21]