There have been a growing number of studies showing that cognitive behavioural treatment packages for children with anxiety disorders are highly effective. Clinically, it is often assumed that treatment outcome is less successful, or that treatment needs to be altered when faced with the existence of comorbid conditions. To date, only one study has directly addressed this question in the child anxiety literature. The present study compared the treatment outcome and maintenance following a brief, group program for the reduction of child and adolescent anxiety disorders in anxious children with versus without comorbid disorders. There was no significant difference in response to treatment at the end of the program and few differences at 12-month follow-up. The only indication of an impact of comorbidity was a suggestion that children with a comorbid condition did not do as well at follow-up. However, this result was only shown on some parent-report measures and not on self-report measures. Overall, the results indicate that treatment for child and adolescent anxiety disorders produces broadly comparable results regardless of the existence of comorbid disorders.