The investigators will recruit 50 patients with idiopathic Parkinson's disease from the department of Neurology of Cliniques universitaires Saint-Luc (Brussels, Belgium) The study is approved by the ethics committee. All patients will give informed written consent to the study. Eligibility criteria are: diagnosis idiopathic Parkinson (according to the Brain Bank criteria of the United Kingdom Parkinson's Disease Society), disease severity (according to modified Hoehn & Yahr stages I to IV), absence of dementia (Minimal Mini Mental State Examination score of 24 or higher), stable drug usage in the last 4 weeks and adequate vision and hearing, achieved using corrective lenses and/or hearing aid if required. Patients will be excluded if they have severe co-morbidity, other neurological problems, acute medical problems (e.g. MI, diabetes) and joint problems affecting mobility, and unpredictable "Off"-periods (score >2, MDS-UPDRS item 4.5).