Epidemiology of Parkinson's disease--an overview.Among the white races, the prevalence rates of Parkinson's disease range from 66 to 187 per 100,000 population, through without any obvious geographical pattern. A similar variation is found in the annual incidence rates with estimates from 5 to 24 per 100,000 population. The black races may be partially protected against the disease. Both sexes are probably equally affected by the disease. Parkinson's disease usually begins after the age of 50 years, and the risk of the disease steeply rises with advancing age. Parkinson's disease is often omitted in death certificates; mortality rates with Parkinson's disease as an underlying cause of death vary from 0.5 to 3.8 per 100,000. Levodopa treatment, by reducing the excess mortality accompanying the natural course of Parkinson's disease, may increase the number of patients living with this disease in the near future. Postencephalitic Parkinson's disease, developing as a sequel to lethargic encephalitis and accounting for some two thirds of parkinsonian cases shortly after the epidemic, has probably been a transient phase in the epidemiology of Parkinson's disease and is now disappearing. Data from epidemiological investigations have advanced our understanding of the cause of Parkinson's disease only to a small extent. No other characteristic than race has been found to influence the susceptibility to the disease. The environmental risks for Parkinson's disease have not been unequivocally demonstrated. Highly conflicting information is available as to the contribution of hereditary to the pathogenesis of Parkinson's disease. Seroepidemiological investigations have shown an increased antibody response against herpes simplex virus in parkinsonian patients, but attempts to detect herpes virus specific products or DNA sequences in the brain material have been unsuccessful.