 Despite advances in pharmacological and behavioral therapies for OCD, a substantial number of patients fail to improve significantly following years of conventional and experimental interventions. For some patients, stereotactic neurosurgery is the only promising option available. Although this procedure has relatively few side effects in the majority of OCD patients and may lead to enduring benefits, its effects on brain tissue and function are irreversible. Bilateral deep brain stimulation DBS is an adjustable and partially reversible procedure that may be a more effective treatment for patients with OCD. This study will determine the effectiveness, safety, and tolerability of DBS in patients with treatment-refractory OCD. 