This study evaluated the psychometric properties of the Children's Yale–Brown Obsessive-Compulsive Scale (CY-BOCS). A total of 61 children and adolescents, aged 4–18 years, who were diagnosed with obsessive-compulsive disorder (OCD) participated. Thirty-seven of these children also participated in a second CY-BOCS administration by the same rater an average of 41 days later. Good internal consistency and test–retest reliability were found for the CY-BOCS Obsession and Compulsion Severity Scores and the Total Score. CY-BOCS scores demonstrated strong correlations with clinician-rated measures of impairment, obsessions, and compulsions. In addition, CY-BOCS scores were moderately related to measures of depression, aggressive behavior, and symptoms of attention deficit hyperactivity disorder, but were not significantly related to clinician ratings of tics or self-reports of general anxiety. Findings suggest that the CY-BOCS is a reliable and valid instrument for the assessment of childhood obsessions and compulsions.