Importance Childhood anxiety is common. Multiple treatment options are available, but existing guidelines provide inconsistent advice on which treatment to use. Objectives To evaluate the comparative effectiveness and adverse events of cognitive behavioral therapy (CBT) and pharmacotherapy for childhood anxiety disorders. Data Sources We searched MEDLINE, EMBASE, PsycINFO, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and SciVerse Scopus from database inception through February 1, 2017. Study Selection Randomized and nonrandomized comparative studies that enrolled children and adolescents with confirmed diagnoses of panic disorder, social anxiety disorder, specific phobias, generalized anxiety disorder, or separation anxiety and who received CBT, pharmacotherapy, or the combination. Data Extraction and Synthesis Independent reviewers selected studies and extracted data. Random-effects meta-analysis was used to pool data. Main Outcomes and Measures Primary anxiety symptoms (measured by child, parent, or clinician), remission, response, and adverse events. Results A total of 7719 patients were included from 115 studies. Of these, 4290 (55.6%) were female, and the mean (range) age was 9.2 (5.4-16.1) years. Compared with pill placebo, selective serotonin reuptake inhibitors (SSRIs) significantly reduced primary anxiety symptoms and increased remission (relative risk, 2.04; 95% CI, 1.37-3.04) and response (relative risk, 1.96; 95% CI, 1.60-2.40). Serotonin-norepinephrine reuptake inhibitors (SNRIs) significantly reduced clinician-reported primary anxiety symptoms. Benzodiazepines and tricyclics were not found to significantly reduce anxiety symptoms. When CBT was compared with wait-listing/no treatment, CBT significantly improved primary anxiety symptoms, remission, and response. Cognitive behavioral therapy reduced primary anxiety symptoms more than fluoxetine and improved remission more than sertraline. The combination of sertraline and CBT significantly reduced clinician-reported primary anxiety symptoms and response more than either treatment alone. Head-to-head comparisons were sparse, and network meta-analysis estimates were imprecise. Adverse events were common with medications but not with CBT and were not severe. Studies were too small or too short to assess suicidality with SSRIs or SNRIs. One trial showed a statistically nonsignificant increase in suicidal ideation with venlafaxine. Cognitive behavioral therapy was associated with fewer dropouts than pill placebo or medications. Conclusions and Relevance Evidence supports the effectiveness of CBT and SSRIs for reducing childhood anxiety symptoms. Serotonin-norepinephrine reuptake inhibitors also appear to be effective based on less consistent evidence. Head-to-head comparisons between various medications and comparisons with CBT represent a need for research in the field.