- The Obsessive–Compulsive Beliefs Questionnaire-87 (OBQ-87) has been constructed by leading obsessive–compulsive disorder (OCD) experts to assess dysfunctional beliefs typical for OCD patients. The OBQ-87 has recently been revised (Obsessive–Compulsive Beliefs Questionnaire-44 [OBQ-44]) to improve its psychometric properties. The current investigation entailed two goals: (1) to assess the sensitivity of both Obsessive Beliefs Questionnaire (OBQ) versions to treatment change and other OCD measures; and (2) to assess relations between symptom subtypes, OBQ beliefs and changes in beliefs as a consequence of treatment. One hundred and four patients have completed the OBQ before and after 12 sessions of behaviour therapy. Results suggest that (1) both OBQ versions exhibit an identical medium effect size; (2) overlap between clinical and non-clinical populations limit the use of the OBQ as a primary measure of treatment change; and (3) the symptom dimension obsessions + checking was related to initial OBQ scores, but no symptom dimensions were related to OBQ pre-treatment to post-treatment changes. Copyright © 2009 John Wiley & Sons, Ltd. Key Practitioner Message: Both versions of the OBQ demonstrate similar sensitivity to treatment change; however the clinical utility of this measure is doubtful.