Objective: To examine the efficacy of exposure-based cognitive-behavioral therapy (CBT) plus a structured family intervention (FCBT) versus psychoeducation plus relaxation training (PRT) for reducing symptom severity, functional impairment, and family accommodation in youths with obsessive-compulsive disorder (OCD). Method: A total of 71 youngsters 8 to 17 years of age (mean 12.2 years; range, 8-17 years, 37% male, 78% Caucasian) with primary OCD were randomized (70:30) to 12 sessions over 14 weeks of FCBT or PRT. Blind raters assessed outcomes with responders followed for 6 months to assess treatment durability. Results: FCBT led to significantly higher response rates than PRT in ITT (57.1% vs 27.3%) and completer analyses (68.3% vs. 35.3%). Using HLM, FCBT was associated with significantly greater change in OCD severity and child-reported functional impairment than PRT and marginally greater change in parent-reported accommodation of symptoms. These findings were confirmed in some, but not all, secondary analyses. Clinical remission rates were 42.5% for FCBT versus 17.6% for PRT. Reduction in family accommodation temporally preceded improvement in OCD for both groups and child functional status for FCBT only. Treatment gains were maintained at 6 months. Conclusions: FCBT is effective for reducing OCD severity and impairment. Importantly, treatment also reduced parent-reported involvement in symptoms with reduced accommodation preceding reduced symptom severity and functional impairment. (Contains 2 figures and 4 tables.)