Based on Framingham data, among the most important risk factors predicting coronary heart disease in both women and men are--aside from age--cholesterol, cigarette smoking, and blood pressure. Consistent with the observation that men are more likely to fall victim to coronary heart disease than women is the fact that they also exhibit higher levels of these risk factors when compared to women, at least up to the age of 45. Standardization of risk factor levels and controlling for both levels of risk factors on coronary heart disease probabilities eliminated the sex differential in 45 to 54 year olds of the Framingham Study. However, among the 55 to 74 year olds, the sex differential was not due to differences in levels or impact of the risk factors. It was conceivable that the sex mortality differential at the older ages was due to the sex differential in primary coronary risk factors at the younger ages.