This is a 1-year, open-label, long-term safety extension for patients who have completed prior istradefylline studies 6002-EU-007, 6002-US-013 or 6002-US-018.

Patients with Parkinson's disease with motor complications on levodopa therapy who completed the prior double-blind studies 6002-EU-007, 6002-US-013 or 6002-US-018 are eligible to enter into this 1-year, long-term open safety study with a starting istradefylline dose of 40mg per day.

Inclusion Criteria:

• Completion of study 6002-EU-007, 6002-US-013 or 6002-US-018
• Non-pregnant and either not of childbearing potential or using specified contraception

Exclusion Criteria:

• History of psychotic illness
• Variant/atypical Parkinson's disease
• Cancer within 5 years of enrollment
• ALT/AST levels > 1.5 times ULN
• Seizure disorder
• Neuroleptic malignant syndrome