Prevalence rates in all 3-year-old children in Fuchu/Tokyo, for a 6-year survey from 1974 to 1980 (total number examined, 17,044), were 8.3% for febrile convulsion and 0.9% for afebrile convulsion. The figures in boys were higher than in girls for febrile convulsion (9.0%:7.5%), but for afebrile convulsion (0.9%:0.9%). Prevalence in a Miyake Island survey for 10 years, from 1973 to 1982 (total number examined, 543) was 9.9% for febrile and 0.4% for afebrile convulsion. Correlations among prevalence of febrile convulsion, epilepsy, and epileptic EEG abnormality in healthy children were inconsistent in geographically isolated villages identified in Miyake Island.