Obsessive-compulsive disorder (OCD) is a chronic debilitating anxiety disorder significant in intrusive thoughts and compensation repetitive behaviors. Few studies have reported on this condition Asia. This study estimated the prevalence, incidence and psychiatric comorbidities of OCD in Taiwan. We identified study subjects for 2000-2008 with a principal diagnosis of OCD according to the International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) diagnostic criteria by using National Health Research Institute database. These patients received either outpatient or inpatient care for their condition. Rates were directly age- and sex-adjusted to the 2004 Taiwan population distribution. The estimated mean annual incidence was 27.57 per 10(5) inhabitants and the one year prevalence was 65.05 per 10(5) inhabitants. Incidence and prevalence increased with age, peaking at age 18-24 years in males and at 35-44 years in females. About 53% of adults (>= 18 years) and 48% of child and adolescent patients (6-17 years) had one or more comorbid psychiatric conditions. The most common comorbid diagnosis was depressive disorders for both adult and child-adolescent patients. We found a lower prevalence and incidence of clinically diagnosed OCD than that of community studies. Many Asian patients with OCD also had various psychiatric comorbidities, a clinically relevant finding. (C) 2014 Elsevier Ireland Ltd. All rights reserved.