ABSTRACT: This study evaluated the effectiveness of the first year of Safer Choices, a theoretically based, multicomponent HIV, STD, and pregnancy prevention program for high school youth. The study featured a randomized trial involving 20 schools in California and Texas, with a cohort of 3,869 ninth-grade students. Students who completed both the baseline and the first follow-up survey approximately seven months later were included in the analysis (n = 3,677). Safer Choices enhanced 9 of 13 psychosocial variables including knowledge, self efficacy for condom use, normative beliefs and attitudes regarding condom use, perceived barriers to condom use, risk perceptions, and parent-child communication. Safer Choices also reduced selected risk behaviors. Specifically, Safer Choices reduced the frequency of intercourse without a condom in the three months prior to the survey, increased use of condoms at last intercourse, and increased use of selected contraceptives at last intercourse.