To evaluate the safety and efficacy of two dose ranges of safinamide (High Dose: 150 to 200 mg/day and Low Dose: 50 to 100 mg/day) orally, as compared to Placebo, as add-on therapy in patients with early idiopathic Parkinson's disease who are currently receiving a stable dose of a single dopamine agonist. It is hypothesized that, over a 24-week period, add-on treatment with safinamide will result in greater improvement of motor symptoms in these patients, compared to treatment with a dopamine agonist alone.

Inclusion Criteria:

• Patients with a diagnosis of idiopathic Parkinson's disease of less than 5 years duration, and a Hoehn and Yahr Stage of I to III,
• who were receiving treatment with a single dopamine agonist at a stable dose for at least 4 weeks prior to Visit 1 (Screening).

Exclusion Criteria:

• Patients with medical conditions and/or taking concomitant medications that would have put them at risk, interfered with the study evaluations, or made them unable to complete the requirements of the study;
• patients with a diagnosis or recent history of substance abuse,
• a history of psychosis,
• who were depressed,
• had evidence of dementia or cognitive dysfunction,
• or who were experiencing end of dose wearing-off;
• female patients of childbearing potential;
• patients who have previously received safinamide.