Two earlier studies of prognosis of coronary heart disease among men enrolled in the Health Insurance Plan in the 1960s and 1970s permitted us to examine whether prognosis had improved over this ten-year period. The new comparison involved 1,133 men aged 35 to 64 years who had survived a first acute myocardial infarction and were followed up for mortality after a baseline examination. Mortality estimates were controlled for clinical and demographic differences between the two cohorts by multivariate methods and by comparing subgroups. The analyses showed no difference in long-term prognosis between patients in the two decades. The observations in this population suggest that any contribution of improved medical care to the nationally observed secular decline in mortality from coronary heart disease in the time period studied was probably restricted to the acute stage of myocardial infarction.