Deep brain stimulation (DBS) is an established therapy for movement disorders and an investigational treatment in other neurologic conditions and in neuropsychiatry. DBS can target with precision neuroanatomical targets deep within the brain that are proposed, on the basis of increasing evidence from functional neuroimaging and other methods, to be centrally involved in the pathophysiology of some neuropsychiatric illnesses. DBS is nonablative, offering the advantages of reversibility and adjustability. In theory, this characteristic might permit therapeutic effectiveness to be enhanced or side effects to be minimized. Although its mechanisms of action are unknown, several possible effects have been proposed to underlie the therapeutic effects of DBS in movement disorders, and potentially in other conditions as well. This issue is the subject of very active investigation in a number of clinical and preclinical laboratories. DBS may offer a degree of hope for patients with intractable neuropsychiatric illness. Research intended to realize this potential will require a very considerable commitment of resources, energy, and time across disciplines including psychiatry, neurosurgery, neurology, neuropsychology, and bioethics. Investigations in this area should proceed cautiously.