The classical perception of Parkinson's disease (PD) heavily emphasises its motor aspects, cognitive features and dementia associated with the disease being largely ignored. Epidemiological studies performed in the last few decades revealed the substantially high incidence and prevalence of cognitive impairment and dementia in PD. Clinical studies using
EpidemiologyDementia associated with PD has been increasingly better recognised, probably because patients with PD survive for longer than before thanks to modern treatment. Although subtle cognitive deficits can be found in newly diagnosed patients with PD, 1 dementia itself is strongly associated with advanced age and severe disease. 2 In population-based, cross-sectional studies the prevalence of dementia has been reported to be 28-41%. A meta-analysis of 12 carefully selected studies revealed a cross-sectional prevalence of close to 30%. 3 The incidence increases up to six-fold and the cumulative incidence over eight years of follow-up was described to be 78%. 4,5 The longitudinal Sydney study revealed that 15 years after the diagnosis 85% of the patients had cognitive impairment, with 50% fulfilling