A meta-analysis was performed to examine the effects of 14 behavioral and social interventions for heterosexual adults on their adoption of safer sex behaviors or incidence of sexually transmitted diseases (STDs). The intervention studies were identified through a systematic search and review strategy. Data were extracted and combined by using well-defined methods and appropriate statistical techniques. For inclusion in this article, studies had to be based in the United States, written in English, first reported between 1988 and 1996, and aimed at reducing sex-related HIV risks. In addition to measuring behavioral or STD incidence outcomes, studies also had used experimental or quasi-experimental designs with control or comparison groups and reported sufficient outcome data to allow calculation of odds ratios. The meta-analytic results show statistically significant effects in reducing sex-related risks (10 studies; odds ratio [OR], 0.81; 95% confidence interval [CI], 0.69-0.95), particularly non-use of condoms (8; OR, 0.69; 95% CI, 0.53-0.90). The interventions also had significant effects in reducing STD infections (6 studies; OR, 0.74; 95% CI, 0.62-0.89). These analyses indicate that science-based prevention interventions have positive effects among populations at risk through heterosexual transmission and that these positive effects are found with biologic and self-reported behavioral measures.