Prevalence of Parkinson's disease in Hokkaido, the northernmost island of Japan.

The prevalence of Parkinson's disease (PD) was investigated in Hokkaido, the northernmost island of Japan. A pilot case-finding study was carried out to estimate the prevalence in the entire island of Hokkaido (population = 5,643,647) initially, then we surveyed the prevalence at one of the smaller cities, Iwamizawa City (population = 80,417). We ascertained 5,342 cases with PD in Hokkaido and 77 cases in Iwamizawa City, estimating the crude prevalence of 94.7/100,000 in Hokkaido (June 30, 1993) and 95.8/100,000 in Iwamizawa City (April 1, 1994), respectively. We calculated that the crude prevalence rate of PD in Japan in currently close to 100/100,000, but the age-adjusted prevalence is still low, compared with those in Europe and North America.