To identify the mode of delivery, communicator, and content dimensions that make STI/HIV prevention interventions most successful at increasing condom use/protected sex or reducing STI/HIV incidence. A literature search for published meta-analyses of STI/HIV prevention interventions yielded 37 meta-analyses that had statistically tested the moderating effects of the dimensions. Significant and non-significant moderators from the coded dimensions were extracted from each meta-analysis. The most consistently significant moderators included matching the gender or ethnicity of the communicator to the intervention recipients, group targeting or tailoring of the intervention, use of a theory to underpin intervention design, providing factual information, presenting arguments designed to change attitudes, and providing condom skills and intrapersonal skills training. The absence of significant effects for intervention duration and expert delivery are also notable. The success of HIV/STI prevention interventions may be enhanced not only by providing skills training and information designed to change attitudes, but also by ensuring that the content is tailored to the target group and delivered by individuals of the same gender and ethnicity as the recipients