BACKGROUND: Prenatal and postnatal probiotic supplementation for prevention and treatment of pediatric atopic dermatitis (PAD) has been studied in clinical trials, but results have been mixed and hindered by heterogeneity of study design. OBJECTIVES: To summarize and interpret quantitatively clinical trial findings on the efficacy of probiotics for PAD and to define key trial features correlating with high methodologic quality. METHODS: PubMed and Cochrane database searches yielded 21 trials (n = 1898; age 0-13 y) published between February 1997 and May 2007 for review and quality assessment. Ten double-blind randomized controlled clinical trials were meta-analyzed by using RevMan. Data from the 6 prevention studies (n = 1581) and 4 treatment trials (n = 299) were pooled by using fixed-effects and random-effects models of relative risk ratios and of weighted mean difference, respectively. RESULTS: Prevention corresponded with summary effect sizes of 0.69 (0.57, 0.83) and 0.66 (0.49, 0.89), respectively, supporting probiotics' PAD prevention potential, which decreased further to 0.61 after exclusion of the 1 trial of postnatal-only probiotics. The clinical significance of the treatment trial findings of intergroup Scoring Atopic Dermatitis (quantification of PAD severity) score reduction by -6.64 points (-9.78, -3.49) and -8.56 (-18.39, 1.28), and intragroup change of -1.06 (-3.86, 1.73) and -1.37 (-4.81, 2.07), is questionable. CONCLUSION: Current evidence is more convincing for probiotics' efficacy in prevention than treatment of PAD.