Six hundred and fifty-eight autopsy cases of both sexes in a general population of Hisayama town (autopsy rate 85%) were examined to determine the frequency and causes of sudden and unexpected death. Seventy-three sudden deaths (11.1%) were identified when sudden death was defined as death occurring within 24 hours after the onset of clinical symptoms. Thirty-nine deaths (54%) were due to intracranial hemorrhage (cerebral and subarachnoid) and 17 (23%) were due to coronary heart disease. An instantaneous death occurred within one hour was observed in 20 of the 73 cases (27%), of which 8 were attributed to coronary heart disease (40%) and one (0.5%) to subarachnoid hemorrhage. Pathologic evidence of recent myocardial infarcts or coronary thrombosis was found less frequently in cases who died within one hour than in those who died between one and 24 hours. An annual incidence of sudden death due to various etiologies, calculated from the population study on Hisayama residents who were aged 40 or over, was 1.7/1,000. Deaths from coronary heart disease in this community were much less common as compared with those reported in Western communities.