 Deep Brain Stimulation DBS is a promising therapy for Parkinsons disease PD. Whether DBS is superior to comprehensive best medical therapy or whether some patients or symptoms respond better to DBS in one area of the brain or the other is currently not known. The goals of this project are to compare the effectiveness of DBS and comprehensive medical therapy as treatments for PD, and to compare bilateral DBS at 2 areas of the brain--the subthalamic nucleus STN and the globus pallidus Gpi--to determine the most effective brain site for surgical intervention In this prospective, randomized, multi-center trial, 316 patients will be enrolled at 13 centers over four and a half years. Patients will initially be randomized to immediate surgery DBS or to 6 months of best medical therapy. BMT patients will then proceed into the surgical phase of the trial. The DBS site STN or GPi will be assigned on a random basis at the time the patient enters the surgical phase of the trial. Patients will be followed for two years post surgery 24-30 months. Effective 080505, randomization to the BMT arm has been discontinued since the study has sufficient information to compare the outcomes of DBS and BMT patients at 6 months. The findings will be critically important in establishing the optimal surgical treatment of the disabling symptoms of PD. 