We studied the behavioral, cognitive, and neuroimaging characteristics of obsessive-compulsive disorder (OCD) in 13 patients with focal brain lesions (acquired OCD) and compared their clinical features and the severity of obsessive and compulsive (OC) symptoms with patients with idiopathic OCD. Both OCD groups were further compared with matched normal controls on a series of neuropsychological tests. Patients with acquired OCD had a negative familial history and later age at onset of OCD symptoms than patients with idiopathic OCD. The two OCD groups showed relatively similar clinical phenomenology, severity of OC symptoms, and profile of neuropsychological deficits. Compared with normal control subjects, both OCD groups showed cognitive deficits affecting attention, intellectual function, memory, word retrieval, and motor and executive functions. Eight of the 13 patients with acquired OCD had abnormal neurologic examinations, whereas only 3 of the 13 patients with idiopathic OCD had abnormal neurologic examinations. Neuroimaging in the acquired OCD group disclosed a variety of lesions involving exclusively the cerebral cortex (frontal, temporal, or cingulate regions), the basal ganglia, or both. These results suggest that acquired and idiopathic OCDs may share a common pathophysiologic mechanism, and that structural damage to specific frontal-limbic-subcortical circuits plays an important role in the pathogenesis of acquired OCD.