The autopsy findings of sudden deaths of school children revealed that the main causes of death were latent myocarditis and arrhythmia, followed by idiopathic cardiomyopathy. The incidence of sudden death of school children in recent years is gradually increasing and 150 cases of sudden death occurred during the 1983 school year. A high incidence of sudden death in senior high school students was found. Sudden cardiac death accounted for approximately 80% of total deaths. The incidence of sudden cardiac death revealed prominent regional differences in Japan. The average for deaths was 0.40/100,000 children/5 years and the highest prefecture revealed 0.70 and the lowest 0.07. The cause of such differences is not clear and requires further analysis.