Despite advances in pharmacotherapy and psychotherapy for major depression, a substantial number of patients fail to improve significantly even after years of conventional and experimental interventions. Bilateral deep brain stimulation (DBS) to the region of the anterior capsule/ventral striatum is an adjustable and reversible procedure that may be a more effective treatment for patients with major depression. This study will determine the effectiveness, safety, and tolerability of DBS in patients with treatment-refractory major depression.