Studies on predictive factors of the obsessivecompulsive disorder response to pharmacologic treatment, specifically clomipramine, are relatively scarce. Forty-five patients treated for a mean period of 18.6 months were classified as having poor response, intermediate response and excellent response, defined by change scores on the Yale-Brown Obsessive-Compulsive Scale. Poor and intermediate response patients were grouped together and compared with the excellent response subgroup. Univariate analysis showed length of illness, family history (siblings), initial compulsiveness score, and cleaning rituals as significant predictors. Two multiple regression analyses with these as independent or predictive variables showed higher initial scores on the Yale-Brown Obsessive-Compulsive Scale associated with poorer response to treatment but, most importantly, cleaning rituals as a predictor of poor or modest response to clomipramine. It may be important for the clinician to assess cleaning habits separately from the more frequently mentioned obsessive-compulsive symptom, hand washing. This distinction may have important clinical, therapeutic, and prognostic implications. © 1993 by Williams and Wilkins.