The 25-item Clark-Beck Obsessive-Compulsive Inventory (CBOCI) was developed to assess the frequency and severity of obsessive and compulsive symptoms. The measure uses a graded-response format to assess core symptom features of obsessive-compulsive disorder (OCD) based on Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) criteria and current cognitive-behavioral formulations. Revisions were made to the CBOCI on the basis of psychometric and item analyses of an initial pilot study of clinical and nonclinical participants. The construct validity of the revised CBOCI was supported in a subsequent validation study involving OCD, nonobsessional clinical, and nonclinical samples. A principal-factor analysis of the 25 items found 2 highly correlated factors of Obsessions and Compulsions. OCD patients scored significantly higher on the measure than nonobsessional anxious, depressed, and nonclinical samples. The questionnaire had strong convergent validity with other OCD symptom measures but more modest discriminant validity.