Context: In several studies, authors have reported on cognitive behavioral therapy (CBT) for children and adolescents with autism spectrum disorders (ASDs), but inconsistent treatment effectiveness was revealed from these studies. Objective: To evaluate the effectiveness of CBT on the symptoms of ASD and social-emotional problems in children or adolescents with ASD by using a meta-analytic approach. Data sources: Data sources included PubMed, Embase, and the Cochrane Library. Study selection: We selected randomized controlled trials (RCTs) in which authors reported effectiveness of CBT on the symptoms of ASD and social-emotional problems in children or adolescents with ASD from database inception to May 2019. Data extraction: For each study, 2 authors extracted data on the first author's surname, publication year, country, sample size, mean age, CBT target, intervention, outcome measurement, follow-up duration, and investigated outcomes. Results: Forty-five RCTs and 6 quasi RCTs of 2485 children and adolescents with ASDs were selected for the final meta-analysis. There was no significant difference between CBT and control for symptoms related to ASD based on self-reported outcomes (standard mean difference: -0.09; 95% confidence interval: -0.42 to 0.24; P = .593), whereas CBT significantly improved the symptoms related to ASD based on informant-reported outcomes, clinician-rated outcomes, and task-based outcomes. Moreover, the pooled standard mean differences indicated that CBT has no significant effect on symptoms of social-emotional problems based on self-reported outcomes. Limitations: The quality of included studies was low to modest, significant heterogeneity among the included studies for all investigated outcomes was detected, and publication bias was inevitable. Conclusions: These findings indicate that CBT may significantly improve the symptoms of ASD and social-emotional problems in children or adolescents with ASD.