A cohort of 7,591 middle-aged Hawaiian-Japanese men free at initial examination of evidence of coronary heart disease or stroke were followed starting in 1965. Between 1965 and 1983, 1,342 of these men died; 229 deaths occurred less than 24 hours after the onset of the terminal episode, of which 98 deaths occurred in less than one hour. In the category of deaths occurring less than one hour after onset, the risk characteristics of those whose deaths were attributed to coronary heart disease and those whose deaths were attributed to an unknown cause were similar. It is appropriate to combine them as "sudden cardiac death." In the category of deaths occurring one to 24 hours after onset, the risk characteristics of those whose deaths were attributed to coronary heart disease and those whose deaths were attributed to an unknown cause differed. It is not appropriate to assume coronary heart disease as the underlying cause of death in this unknown cause group. The predictors of sudden cardiac death were blood pressure, serum cholesterol, serum glucose, cigarette smoking, history of parental heart attack, and electrocardiographic evidence of left ventricular hypertrophy or strain. Inversely related to risk were alcohol intake and the number of years spent in Japan. No factor distinguished those at risk for sudden cardiac death from those at risk for other manifestations of coronary heart disease.