The incidence and some risk factors of Parkinson's disease were investigated in a study performed in The Netherlands. The study was based on a disease register of the Sentinel Stations, which provide a complete ascertainment of new patients with Parkinson's disease in 60 general practices in The Netherlands. The incidence rate of Parkinson's disease in The Netherlands is estimated to be 11/100,000 person-years for men and 12/100,000 person-years for women. Risk factors for Parkinson's disease were investigated in a case-control study in which 86 cases, with the diagnosis of Parkinson's disease confirmed by a neurologist, were compared with 172 reference subjects, matched for age and gender. Cigarette smoking was associated with a lower risk of Parkinson's disease (relative risk 0.6, 95% confidence interval 0.3-1.0). No association was observed between Parkinson's disease and severe head trauma with loss of consciousness, or surgery with total anaesthesia.