The survey of sudden death (SD), defined as death within 24 hours from the onset of underlying cause, was conducted in Niigata. The survey was based on all summary death certificates for the period 1984 to 1986. The underlying cause was divided into 4 groups: acute myocardial infarction (AMI), cerebrovascular accident (CVA), other circulatory diseases (OCD) and non-circulatory disease (NCD). The SD incidence ratio of male to female was 1.7, 1.3, 1.3, and 1.5 for AMI, CVA, OCD, and NCD, respectively. OCD accounted for 50.1% of underlying causes in male and 53.1% in female. The proportion of OCD cases with histories of diseases related to atherosclerosis (e.g. hypertension, diabetes, etc) increased with age in both sexes, accounting for 38.5% in male and 36.4% in female aged 75 years old or over.