Inclusion Criteria:

• Patients must have a clinical diagnosis of probable idiopathic PD.
• Demonstrated response to dopaminergic therapy, defined as demonstrating at least 30% improvement in parkinsonian motor signs, based upon the UPDRS motor examination subscore, following the administration of their DA drug(s) during the screening neurological examination.
• Hoehn and Yahr (H&Y) stage II when OFF medication.
• No contraindications to surgery.
• Age between 50 and 75 years old.
• Available for follow-up for four years.
• Informed Consent: The subject understands the risks, benefits, and alternatives to the study procedures and participation in the study.
• MRI within normal range for age.
• Levodopa or dopamine agonist therapy for greater than six months but less than or equal to four years.

Exclusion Criteria:

• Evidence of an alternative diagnosis or secondary parkinsonism, as suggested by features unusual early in the clinical course: Prominent postural instability, freezing phenomena, or hallucinations unrelated to medications in the first 3 years after symptom onset; dementia preceding motor symptoms; supranuclear gaze palsy (other than restriction of upward gaze) or slowing of vertical saccades in the first year; severe, symptomatic dysautonomia unrelated to medications; documentation of a condition known to produce parkinsonism and plausibly connected to the subject's symptoms (such as suitably located focal brain lesions or neuroleptic use within the past 6 months)
• Uncontrolled medical condition or clinically significant medical disease that would increase the risk of developing pre- or postoperative complications (e.g., significant cardiac or pulmonary disease, uncontrolled hypertension).
• Evidence of dementia
• Major psychiatric disorder
• Previous brain operation or injury.
• Active participation in another clinical trial for the treatment of PD.
• Patients who have demand cardiac pacemakers or implantable cardioverter defibrillators (ICD's).
• Patients who have medical conditions that require repeat MRI scans or diathermy treatments.
• Evidence of existing dyskinesias or motor fluctuations.