Objective: The purpose of the present study was to evaluate the influence of comorbid disorders on the degree of change and the endpoint of cognitive-behavioral treatment in anxious young people. Method: Data on 750 children 6 to 18 years old were compiled from different samples within one clinic. All children had a primary anxiety disorder and were engaged in a manual-based, 10-session, cognitive-behavioral treatment program. Outcome was determined according to diagnostic status and continuous symptom measurements. Analyses compared results among four groups: no comorbidity, comorbid anxiety disorders, comorbid externalizing disorders, comorbid mood disorders. All analyses were intent-to-treat analyses. Results: Children with comorbid depression were the least likely to be free of their primary anxiety diagnosis at the end of treatment and follow-up. According to child and maternal reports, symptoms of anxiety decreased similarly over time in all groups, but children with comorbid mood disorders scored significantly highest at all time points. Examining the effects of anxiety treatment on comorbid disorders showed that comorbid mood disorders, but not externalizing disorders, decreased significantly over time. Conclusions: The existence of comorbid disorders does not appear to affect the rate or extent of response to cognitive-behavioral treatment for child anxiety. However, comorbidity has a marked influence on the endpoint of treatment. Children with nonanxiety comorbidity and especially with comorbid mood disorders exhibit greater severity at the outset and remain worse after treatment. On the positive side, treatment for anxiety disorders appears to decrease comorbid mood disorders, although it has less effect on comorbid externalizing disorders. (Contains 3 tables.)