BACKGROUND: The effects of Web- and computer-based smoking cessation programs are inconsistent in randomized controlled trials (RCTs). We evaluated those effects using a meta-analysis. METHODS: We searched MEDLINE (PubMed), EMBASE, and the Cochrane Review in August 2008. Two evaluators independently selected and reviewed eligible studies. RESULTS: Of 287 articles searched, 22 RCTs, which included 29 549 participants with 16 050 enrolled in Web- or computer-based smoking cessation program groups and 13 499 enrolled in control groups, were included in the final analyses. In a random-effects meta-analysis of all 22 trials, the intervention group had a significant effect on smoking cessation (relative risk [RR], 1.44; 95% confidence interval [CI], 1.27-1.64). Similar findings were observed in 9 trials using a Web-based intervention (RR, 1.40; 95% CI, 1.13-1.72) and in 13 trials using a computer-based intervention (RR, 1.48; 95% CI, 1.25-1.76). Subgroup analyses revealed similar findings for different levels of methodological rigor, stand-alone vs supplemental interventions, type of abstinence rates employed, and duration of follow-up period, but not for adolescent populations (RR, 1.08; 95% CI, 0.59-1.98). CONCLUSION: The meta-analysis of RCTs indicates that there is sufficient clinical evidence to support the use of Web- and computer-based smoking cessation programs for adult smokers.