This article describes a factor analytically derived, self-report instrument - the Schedule of Compulsions, Obsessions, and Pathological Impulses (SCOPI) - using data from college students, adults, psychiatric outpatients, and patients with obsessive-compulsive disorder (OCD). The five SCOPI scales all are internally consistent (with coefficient alphas of .80 and higher) and are strongly stable across a 2-month interval (with retest correlations ranging from .79 to .82). They also show good convergent and adequate discriminant validity (a) when correlated with other OCD measures and (b) in analyses of self-ratings versus spouse ratings. Additional analyses indicate that three scales - Obsessive Checking, Obsessive Cleanliness, and Compulsive Rituals - assess core symptoms of OCD. The two remaining scales - Hoarding and Pathological Impulses - appear to tap different (but related) constructs.