Background. A greater understanding of the determinants of risky behaviors is an essential precursor to the development of successful AIDS prevention programs for adolescents. Methods. A survey measuring AIDS-related behaviors, beliefs, and knowledge was administered to a sample of 531 10th-grade students residing in an AIDS epicenter. Results. Of the 56.8% of students reporting past-year involvement in sexual intercourse, 67.3% reported unprotected intercourse with low-risk partners, 1.3% reported unprotected intercourse with high-risk partners, and 6.6% reported a past-year history of a sexually transmitted disease. Students whose friends had intercourse and never or inconsistently used condoms, who personally sanctioned intercourse involvement, who believed that the majority of their peers had intercourse, and who perceived low preventive action self-efficacy, were 5.1, 3.0, 2.1, 3.7, and 2.8 times more likely, respectively, to score in the riskier categories of an AIDS behavior index. Conclusions. These findings suggest that addressing socioenvironmental influences on risky and preventive behaviors may prove to be the most effective AIDS prevention strategy among adolescents.