Objective: To examine the optimal Children's Yale-Brown Obsessive-Compulsive Scale (CY-BOCS) percent reduction cutoffs for predicting treatment response and clinical remission among children and adolescents with obsessive-compulsive disorder (OCD). Method: Youth with OCD (N = 109; range 7 to 19 years) received 14 sessions of weekly or intensive family-based CBT as part of previously published studies or through the standard clinical flow at our facility. Assessments were conducted before and after treatment and included the CY-BOCS, response and remission status on the Clinical Global Impressions Scale, and the Child Obsessive-Compulsive Impact Scale. Results: Maximally efficient CY-BOCS cutoffs were observed at a 25% reduction for treatment response, a 45% to 50% reduction for symptom remission, and a CY-BOCS score of 14 when considering raw scores. OCD-related impairment improved as a function of treatment response and symptom remission. Conclusions: These data indicate that a CY-BOCS reduction of 25% appears to be optimal for determining treatment response, a reduction of 45% to 50% appears to be optimal for detecting symptom remission, and a CY-BOCS raw score of 14 best reflects remission after treatment. Clinical trials should employ a consistent definition of treatment response for cross-study comparability. Clinicians can use these values for treatment planning decisions. (Contains 1 figure and 3 tables.)