We conducted a systematic review and meta-analysis to locate, characterize, and summarize effects of behavioral HIV prevention interventions for men who have sex with men (MSM). We found 54 interventions with 16,224 participants that were evaluated in 40 randomized trials and controlled observational studies with independent comparison groups. Formats included 26 small group interventions, 18 individual-level interventions, and 10 community-level interventions. Fifteen interventions focused on HIV-positive individuals including MSM. The 38 interventions that were compared with minimal or no HIV prevention interventions, reduced unprotected sex by 27% (95% confidence interval [CI] = 15-37%). The other 16 interventions reduced unprotected sex by 17% beyond changes observed in standard or other HIV prevention interventions (CI = 5-27%). Behavioral interventions reduce self-reported unprotected sex among MSM.