This study involves the screening and follow-up of individuals with OCD and OCD-related disorders. Participants will be screened with a medical and psychiatric evaluation, questionnaires, and neurological testing. Participants will then have study visits every 4 to 12 weeks to undergo symptom and daily functioning evaluations, personality tests, blood and urine tests, memory tests, brain scans, and other clinical exams. Participants will be assessed with interviews and paper-and-pencil or computer-assisted tests. Participants may have the opportunity to participate in drug studies and to join a monthly OCD support group. At the end of the study, participants will be referred to community or private treatment centers.