The use of deep brain stimulation in psychiatric disorders has received great interest owing to the small risk of the operation, the reversible nature of the technique, and the possibility of optimizing treatment postoperatively. Currently, deep brain stimulation in psychiatry is investigated for obsessive-compulsive disorder, Gilles de la Tourette's syndrome, and major depression. This chapter reviews the application of deep brain stimulation in obsessive-compulsive disorder. Preliminary results suggest that deep brain stimulation in obsessive-compulsive disorder can effectuate a decrease of 40-60% in at least half of the patients. Although various side effects occur, most of these are transitory and linked to specific stimulation parameters which can be changed. Because only a few studies have been performed with a limited number of patients in accordance with varying research protocols, appliance of deep brain stimulation to obsessive-compulsive disorder is still at an experimental stage. The speed of the effect of deep brain stimulation causes fundamental assumptions on the pathophysiology of obsessive-compulsive disorder.