The purpose of this study is to evaluate the safety and efficacy of bilateral stimulation of the subthalamic nucleus (STN) of the brain when using the ANS Totally Implantable Deep Brain Stimulation System as an adjunctive treatment for reducing some of the symptoms of Parkinson's Disease that are not adequately controlled with medication.

This is a prospective, controlled, multi-centered, 12 months post-implantation study. A maximum of 15 sites will enroll a total of 136 patients.

All study participants will have the study device surgically implanted. After implant surgery, study participants will return to the clinic for evaluation 30 days after surgery, three months after surgery, six months after surgery and twelve months after surgery. At the baseline, three, six and twelve month visits the patient's Parkinson's symptoms and ability to perform daily activities will be evaluated using a number of accepted assessment tools including a Dyskinesia diary, evaluation of PD symptoms, quality of life scoring and patient extension study to monitor the safety and efficacy of the ANS Libra/Libra Deep Brain Stimulation System.

After the 1 year study, patients may enter another protocol (C-06-04) to continue to monitor the safety and efficacy of the Libra Deep Brain Stimulation System. Patients may be followed for an additional 4 years.

If necessary, patients may continue to have access to the investigational device under protocol (C-13-02) which allows for compassionate use access to it.

Inclusion Criteria:

• Person is 18 to 80 years of age
• Person has been diagnosed with Parkinson's disease for at lease five (5) years
• Person experiences at least six (6) hours or more daily "off-time" or moderate to severe dyskinesias during waking hours
• Person has a history of improvement of Parkinson's symptoms with l-dopa (levodopa) therapy
• Person must be willing to maintain a constant dose of anti-Parkinson's disease medication for at least one month prior to study enrollment
• Person must be available for appropriate follow-up times for the length of the study

Exclusion Criteria:

• Person has any major illness or medical condition that would interfere with participation in the study
• Person currently suffers from untreated, major depression
• Person has an electrical or electromagnetic implant (e.g. cochlear prosthesis or pacemaker)
• Person has had a prior surgery for the treatment of PD symptoms, including previous DBS surgery
• Person has dementia
• Person has a history of seizures