Deep brain stimulation (DBS) is the surgical procedure of choice for patients with advanced Parkinson’s disease (PD) whose management of symptoms is insufficiently controlled by pharmacological means. However, despite the number of patients that have undergone DBS the precise mechanisms underlying its therapeutic action are unknown. Typically, electrodes are implanted in either the subthalamic nucleus or globus pallidus inserta and stimulation is continuous. Control of motor symptoms is generally good, but the benefits for alleviating non-motor symptoms, as well as improvements in quality of life or psychosocial function are not so clear cut. DBS is also associated with significant unwanted side effects that must be balanced against any observed benefits.