Abstract Background: Treatment programs for overweight and obese young children are of variable effectiveness, and the characteristics of effective programs are unknown. In this systematic review with meta-analysis, the effectiveness of treatment programs for these children is summarized. Methods: PubMed, Embase, Web of Science, and PsycINFO databases were searched up to April 2012. Articles reporting the effect of treatment on the body weight of overweight or obese children with a mean age in the range of 3– <8 years are included. Studies reporting the change in BMI z-score with standard error were included in a meta-analysis. For this purpose, a random-effects model was used. Results: The search identified 11,250 articles, of which 27 were included in this review. Eleven studies, including 20 treatment programs with 1015 participants, were eligible for the meta-analysis. The pooled intervention effect showed high heterogeneity; therefore, subgroup analysis was performed. Subgroup analysis showed that program intensity and used components partly explained the heterogeneity. The subgroup with two studies using multicomponent treatment programs (combining dietary and physical activity education and behavioral therapy) of moderate or high intensity showed the largest pooled change in BMI z-score (–0.46; I2, 0%). Conclusion: Although the subgroup multicomponent treatment programs of moderate to high intensity contained only two studies, these treatment programs appeared to be most effective in treating overweight young children.