CONTEXT: Adolescent pregnancy, HIV, and other sexually transmitted infections (STIs) are major public health problems in the U.S. Implementing group-based interventions that address the sexual behavior of adolescents may reduce the incidence of pregnancy, HIV, and other STIs in this group. EVIDENCE ACQUISITION: Methods for conducting systematic reviews from the Guide to Community Preventive Services were used to synthesize scientific evidence on the effectiveness of two strategies for group-based behavioral interventions for adolescents: (1) comprehensive risk reduction and (2) abstinence education on preventing pregnancy, HIV, and other STIs. Effectiveness of these interventions was determined by reductions in sexual risk behaviors, pregnancy, HIV, and other STIs and increases in protective sexual behaviors. The literature search identified 6579 citations for comprehensive risk reduction and abstinence education. Of these, 66 studies of comprehensive risk reduction and 23 studies of abstinence education assessed the effects of group-based interventions that address the sexual behavior of adolescents, and were included in the respective reviews. EVIDENCE SYNTHESIS: Meta-analyses were conducted for each strategy on the seven key outcomes identified by the coordination team-current sexual activity; frequency of sexual activity; number of sex partners; frequency of unprotected sexual activity; use of protection (condoms and/or hormonal contraception); pregnancy; and STIs. The results of these meta-analyses for comprehensive risk reduction showed favorable effects for all of the outcomes reviewed. For abstinence education, the meta-analysis showed a small number of studies, with inconsistent findings across studies that varied by study design and follow-up time, leading to considerable uncertainty around effect estimates. CONCLUSIONS: Based on these findings, group-based comprehensive risk reduction was found to be an effective strategy to reduce adolescent pregnancy, HIV, and STIs. No conclusions could be drawn on the effectiveness of group-based abstinence education.