A systematic comparison was made of the incidence rates of major coronary heart disease (CHD), defined as fatal and non-fatal myocardial infarction and probable CHD deaths, observed in the Paris Prospective Study, the European and American cohorts of the Seven Countries Study, and the populations of the Pooling Project. The Paris study results were adjusted to the age-distribution and follow-up duration of the other studies. The major CHD incidence rate in the Paris study proved to be intermediate between those observed in Northern and Southern European populations and half to one-third those observed in the American populations. Mean risk-factor levels were of the same order of magnitude as in the whole European group and were lower than in the Pooling Project population, particularly for cholesterol and smoking. The coefficients of risk factors in the multivariate analysis of risk among the four studies showed similar gradients of risk except for a steeper gradient with smoking in the Paris Prospective Study. After adjustment to the risk-factor levels, major CHD incidence in the Paris study was comparable with that in the European population but lower than those in the U.S. Railroad population (ratio of predicted numbers of cases=1.56) and the pooling project population (ratio of predicted numbers of cases=2.24).