The objectives of this trial conducted in early Parkinson's disease (PD) patients are:

• To assess if patients with early Parkinson's disease (PD) can be successfully switched (overnight switching) from Pramipexole (PPX) Immediate Release (IR) to Pramipexole Extended Release (ER). A successful switch at a specific visit is defined as no worsening of the Unified Parkinsons Disease Rating Scale (UPDRS) parts II+III score by more than 15% from baseline and no drug-related adverse events leading to withdrawal;
• To establish if this successful switch can be obtained with or without dose-adaptation;
• To provide information about the conversion ratio (mg:mg) from Pramipexole IR to Pramipexole ER.

Inclusion Criteria:

1. Male or female patient with idiopathic Parkinson's disease (PD) confirmed by at least two of the following signs: resting tremor, bradykinesia, rigidity.
2. Parkinson's disease diagnosed within 5 years.
3. Patients 30 years of age or older at the time of diagnosis.
4. Modified Hoehn and Yahr stage of 1 to 3.
5. Patients receiving pramipexole IR for at least three months prior to baseline visit (randomization visit, V2).
6. Pramipexole dose should be optimized (according investigator¿s judgement), greater or equal to 1.5 mg/day, stable and equally divided 3 times per day, for a least 4 weeks prior to baseline visit (V2).
7. Patients willing and able to comply with scheduled visits, treatment plan, laboratory tests and other study procedures.
8. Signed informed consent obtained before any study procedures are carried out in accordance with International Conference on Harmonization - Good Clinical Practice (ICH-GCP) guidelines and local legislation).

Exclusion Criteria:

1. Motor complications under levodopa therapy at V1.
2. Atypical parkinsonian syndromes due to drugs, metabolic disorders, encephalitis or degenerative diseases.
3. Dementia, as defined by a Mini-Mental State Exam score < 24 at V1
4. Any psychiatric disorder according to Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria
5. History of psychosis, except history of drug induced hallucinations
6. Clinically significant electrocardiogram (ECG) abnormalities at V1.
7. Clinically significant hypotension either at screening visit or at baseline visit.
8. Malignant melanoma or history of previously treated malignant melanoma.
9. Any other clinically significant disease
10. Pregnancy or breast-feeding.
11. Sexually active female of childbearing potential
12. Serum levels of Aspartate Aminotransferase (Serum Glutamic Oxaloacetic Transaminase) (AST (SGOT)), Alanine Aminotransferase (Serum Glutamate Pyruvate Transaminase) (ALT (SGPT)), alkaline phosphatases or bilirubin > 2 Upper Limit of Normal (ULN) (on screening lab test).
13. Patients with a creatinine clearance < 50 mL/min
14. Any dopamine agonist (except pramipexole IR) within three months prior to baseline visit.
15. History of discontinuation of treatment with pramipexole IR
16. Previous treatment with pramipexole ER.
17. Any medication (including intra-muscular formulations) with central dopaminergic antagonist activity within 4 weeks prior to the baseline visit (i.e. typical neuroleptics, atypical antipsychotics, reserpine, methyldopa, centrally-active antiemetics, etc).
18. Any of the following drugs within 4 weeks prior to the baseline visit: methylphenidate, cinnarizine, amphetamines.
19. Flunarizine within 3 months prior to baseline visit.
20. Known hypersensitivity to Pramipexole or its excipients.
21. Drug abuse (including alcohol), according to Investigator¿s judgement, within 2 years prior to screening.
22. Participation in other investigational drug studies or use of other investigational drugs within 4 weeks or five times the half-life of the investigational drug (whichever is longer) prior to baseline visit.

Any publication of the result of this trial must be consistent with the Boehringer Ingelheim publication policy. The rights of the investigator and of the sponsor with regard to publication of the results of this trial are described in the investigator contract.