OBJECTIVE: To examine the relative efficacy of family-based cognitive-behavioral therapy (CBT) versus family-based relaxation treatment (RT) for young children ages 5 to 8 years with obsessive-compulsive disorder (OCD). METHOD: Forty-two young children with primary OCD were randomized to receive 12 sessions of family-based CBT or family-based RT. Assessments were conducted before and after treatment by independent raters blind to treatment assignment. Primary outcomes included scores on the Children's Yale-Brown Obsessive Compulsive Scale and Clinical Global Impressions-Improvement. RESULTS: For the intent-to-treat sample, CBT was associated with a moderate treatment effect (d = 0.53), although there was not a significant difference between the groups at conventional levels. For the completer sample, CBT had a large effect (d = 0.85), and there was a significant group difference favoring CBT. In the intent-to-treat sample, 50% of children in the CBT group achieved remission as compared to 20% in the RT group. In the completer sample, 69% of children in the CBT group achieved a clinical remission compared to 20% in the RT group. CONCLUSIONS: Results indicate that children with early-onset OCD benefit from a treatment approach tailored to their developmental needs and family context. CBT was effective in reducing OCD symptoms and in helping a large number of children achieve a clinical remission.