Objective: To compare the effectiveness of group cognitive-behavioral therapy (GCBT) and of sertraline in treatment-naive children and adolescents with obsessive-compulsive disorder. Method: Between 2000 and 2002, 40 subjects between 9 and 17 years old were randomized to receive GCBT (n = 20) or sertraline (n = 20). GCBT consisted of a manual-based 12-week cognitive-behavioral protocol adapted for groups, and treatment with sertraline involved medication intake for 12 weeks. Subjects were assessed before, during, and after treatment (at 1, 3, 6, and 9 months after treatment conclusion). Primary outcome measure was the Children's Yale-Brown Obsessive-Compulsive Scale. Repeated-measures analyses of variance were done. Results: Both GCBT and sertraline conditions had significant improvement in obsessive-compulsive disorder symptoms as measured by the Children's Yale-Brown Obsessive-Compulsive Scale after 12 weeks of treatment. After the 9-month follow-up period, subjects in the GCBT condition had a significantly lower rate of symptom relapse than those in the sertraline group. Conclusions: The treatment with GCBT may be effective in decreasing obsessive-compulsive symptoms in childhood obsessive-compulsive disorder and should be considered as an alternative to either individual cognitive-behavioral therapy or a medication, such as sertraline. Results support the effectiveness and the maintenance of gains of GCBT in the treatment of youngsters with obsessive-compulsive disorder.