The frequency of and risk factors for sudden death in men and women with and without prior coronary heart disease were investigated in the population-based Framingham Heart Study. The cohort initially consisted of 2,336 men and 2,873 women. Over 26 years, 146 men died suddenly (46% of all male coronary heart disease deaths). A total of 69 men without and 77 men with prior evidence of coronary heart disease were victims of sudden death. Out of 50 sudden deaths in women (34% of female coronary heart disease deaths), 34 occurred in women without prior coronary disease and 16 in women with prior coronary disease. Incidence rates for sudden death were substantially greater in men than in women and in both men and women with, as opposed to without, prior coronary heart disease. The classic coronary heart disease risk factors, left ventricular hypertrophy, age, serum cholesterol, number of cigarettes smoked daily, relative weight, and systolic blood pressure, emerged from multiple logistic regression analysis of sudden death in men without prior coronary heart disease. However, in men with prior coronary disease, only left ventricular hypertrophy and intraventricular block, and no other classic risk factors, were positive predictors of sudden death. For women without prior coronary disease, significant factors were age, vital capacity, hematocrit, serum cholesterol (marginal), and serum glucose (marginal). In women with prior coronary disease, only hematocrit was a consistent predictor. Reasons for the substantial differences in sudden death risk profiles between men and women are not entirely clear, but limitations in data may partially account for these sex differences.