INCLUSION:

• Clinical diagnosis of Idiopathic Parkinson's Disease based on the presence of at least 2 of the cardinal motor signs (akinesia/bradykinesia, rigidity, tremor, and gait/balance disorder) and a clear response to Levo-dopa therapy.
• Hoeh & Yahr staging III or worse "off " medication periods.
• Intractable, disabling motor fluctuations, dyskinesias, or freezing episodes.
• Unsatisfactory clinical response to maximal medical management or previous surgical treatment.
• Stable on Parkinson's medications for at least 30 days with total L-dopa equivalence varying no more than +/- twenty percent during the 30 day period.
• Absence of cognitive, or psychiatric or other co-morbidities that might interfere with the patient's ability to understand and sign the informed consent form.

EXCLUSION:

• Clinically significant medical history that increases pre- / post operative complications (Cardiac or pulmonary disease, uncontrolled hypertension, diabetes…).
• Secondary or atypical parkinsonism as suggested by: i. History of stroke, encephalitis, exposure to toxins or neuroleptics. ii. Neurologic signs of upper motor neuron or cerebella involvement, supranuclear gaze palsy, or significant autonomic dysfunction. iii. MRI scan with evidence of significant brain atrophy, lacunar infracts, or iron deposits in the putamen.
• Dementia as indicated by a Mattis Dementia Rating Scale (DRS) less than 116 or DSM-IV criterion for dementia.
• Clinically significant psychiatric disorder meeting Structured Clinical Interview for the DSM-IV criteria for an active anxiety, depressive, or psychotic disorder.