Nationwide epidemiological surveys of Kawasaki disease have been conducted nine times in Japan since 1970. By the end of 1986, 83 857 (male:female ratio, 1.4) cases were reported. We summarize the results of these surveys, especially the latest survey of cases from January 1985 to December 1986. There were three epidemic years - 1979, 1982, and 1986. The ratios of the number of patients diagnosed in each of those years to the number in the preceding year were 2.0, 2.4, and 1.7, respectively. The last epidemic started in a metropolitan area of Tokyo in December 1985 and propagated northwards and southwards to involve almost all of the country in six months. The age-specific incidence curve showed a unimodal peak at nine to 11 months of age. The proportion of sibling cases was ∼2%. The epidemiological pictures suggested that the disease was caused by an unknown biologic agent that is common in the community and that spreads easily among very young children.