We examined the frequency of dementia and depressive symptomatology in 60 Parkinson's disease (PD) patients, identified in a large representative sample of the population, aged 65 years and older, living at home or in institutions in Gironde, France. Dementia, diagnosed according to DSM-III-R criteria, was present in 17.6%, and depressive symptomatology, assessed by the Center for Epidemiologic Studies-Depression Scale, was present in 32.7%. The frequency of dementia in PD increased strongly with age and was higher in institutionalized PD patients than in those living at home. PD was significantly associated with dementia for individuals living at home (odds ratio = 8.2, adjusted for age and symptoms of depression.