BACKGROUND: Anxiety disorders are common psychiatric conditions affecting children and adolescents. Although cognitive behavioral therapy and selective serotonin-reuptake inhibitors have shown efficacy in treating these disorders, little is known about their relative or combined efficacy. METHODS: In this randomized, controlled trial, we assigned 488 children between the ages of 7 and 17 years who had a primary diagnosis of separation anxiety disorder, generalized anxiety disorder, or social phobia to receive 14 sessions of cognitive behavioral therapy, sertraline (at a dose of up to 200 mg per day), a combination of sertraline and cognitive behavioral therapy, or a placebo drug for 12 weeks in a 2:2:2:1 ratio. We administered categorical and dimensional ratings of anxiety severity and impairment at baseline and at weeks 4, 8, and 12. RESULTS: The percentages of children who were rated as very much or much improved on the Clinician Global Impression-Improvement scale were 80.7% for combination therapy (P<0.001), 59.7% for cognitive behavioral therapy (P<0.001), and 54.9% for sertraline (P<0.001); all therapies were superior to placebo (23.7%). Combination therapy was superior to both monotherapies (P<0.001). Results on the Pediatric Anxiety Rating Scale documented a similar magnitude and pattern of response; combination therapy had a greater response than cognitive behavioral therapy, which was equivalent to sertraline, and all therapies were superior to placebo. Adverse events, including suicidal and homicidal ideation, were no more frequent in the sertraline group than in the placebo group. No child attempted suicide. There was less insomnia, fatigue, sedation, and restlessness associated with cognitive behavioral therapy than with sertraline. CONCLUSIONS: Both cognitive behavioral therapy and sertraline reduced the severity of anxiety in children with anxiety disorders; a combination of the two therapies had a superior response rate. (ClinicalTrials.gov number, NCT00052078.) 2008 Massachusetts Medical Society