The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS; Goodman, Price, Rasmussen, Mazure, Delgado, et al., 1989) is acknowledged as the gold standard measure of obsessive-compulsive disorder (OCD) symptom severity. A number of areas where the Y-BOCS may benefit from revision have emerged in past psychometric studies of the Severity Scale and Symptom Checklist. Therefore, we created the Yale-Brown Obsessive-Compulsive Scale--Second Edition (Y-BOCS-II) by revising the Severity Scale item content and scoring framework, integrating avoidance into the scoring of Severity Scale items, and modifying the Symptom Checklist content and format. One hundred thirty treatment-seeking adults with OCD completed a battery of measures assessing OCD symptom severity and typology and depressive and anxious symptomology. Interrater and test-retest reliability were assessed on a subsample of participants. The Y-BOCS-II showed strong internal consistency for the Symptom Checklist (Kuder-Richardson-20 = 0.91) and Severity Scale ([alpha] = 0.89). Test-retest and interrater reliabilities were both high (intraclass correlations greater than 0.85). Confirmatory factor analyses did not show adequate fit with previous models of the Y-BOCS. Exploratory factor analysis revealed a two-factor solution generally consistent with the Obsession and Compulsion Severity subscales. Construct validity was supported by strong correlations with clinician-rated measures of OCD symptom severity and moderate correlations with measures of worry and depressive symptoms. Taken together, the Y-BOCS-II has excellent psychometric properties in assessing the presence and severity of obsessive-compulsive symptoms. Although the Y-BOCS remains a reliable and valid measure, the Y-BOCS-II may provide an alternative method of assessing symptom presence and severity. (Contains 7 tables and 3 footnotes.)