• A study of the incidence of Parkinson's disease was carried out in a Japanese city, and cases of those who had died were studied to clarify the longevity of the patients and causes of death. On incidence day, April 1, 1980, a total of 101 patients with Parkinson's disease were found to be living in the investigated area, which had a population of 125,291. The incidence rate was 80.6 per 100,000 population, and the average annual incidence for the period 1975 through 1979 was 10.2 per 100,000 population per year. The average age at death was 70.0 years, and the mean duration of illness was 7.4 years. The main causes of death were heart diseases and bronchopneumonia, which were complications of a long period of being bedridden.