Approximately 30,000 patients have been treated throughout the world with deep brain stimulation for Parkinson's disease and other conditions. With accumulating experience, there has been an appreciation of the important benefits of this procedure, including the alleviation of disability and improvement in the quality of life. We have also become aware of some limitations of DBS surgery. Among the important issues that remain to be resolved are the timing of surgery, whether early or late in the course of the disease, and the best target for the individual patient, including a reassessment of the relative merits of globus pallidus versus subthalamic nucleus surgery. A better understanding of the symptoms that are resistant to both levodopa therapy and DBS surgery is also required.