The prevalence of Parkinson’s disease was studied in Izumo City, the Shimane prefecture having the largest population of the elderly in the country. The adult population of Izumo City (56,869 people over 20 years of age) were screened by means of questionnaires sent by mail and by other methods. A total of 66 people, 18 males and 48 females, were found to have Parkinson’s disease. The prevalence of this disease was 82.0/100,000 population, the highest reported in Japan to date. Of the patients affected, 17.1 % showed apparent dementia. Those with dementia were older and were classified at a more advanced Yahr stage than were the nondemented cases. The prevalence of Parkinson’s disease in the growing geriatric population has major medical and socioeconomic implications.