The purpose of this study was to conduct a meta-analysis of computer-mediated interventions (CMIs) aimed at changing theoretical mediators of safer sex. Meta-analytic aggregation of effect sizes from k = 20 studies indicated that CMIs significantly improved HIV/AIDS knowledge, d = 0.276, p less than 0.001, k = 15, N = 6,625; sexual/condom attitudes, d = 0.161, p less than 0.001, k = 12, N = 5,816; and condom self-efficacy, d = 0.186, p less than 0.001, k = 10, N = 3,308. Although assessed in fewer studies, CMIs also significantly increased perceived susceptibility, condom communication, and condom intentions. Effect sizes were found to be of similar magnitude to human-delivered interventions. Exploratory analysis of moderating influences detected few significant variables. Implications for the development and testing of CMIs are discussed.