During 20 years of follow-up of 5,127 men and women initially free of coronary heart disease in the Framingham cohort, 193 men and 53 women had one or more recognized, symptomatic myocardial infarctions. An additional 45 men and 28 women had unrecognized myocardial infarctions. Subsequent mortality and morbidity including angina, reinfarction, congestive failure and sudden death were ascertained. One in five men who had a first myocardial infarction died within 1 year, a mortality rate 14 times that of those free of coronary heart disease. In men who survived the 1st year, a recognized myocardial infarction increased risk of death over the next 5 years to 23 percent, four times that of the general population. The next 5 years carried a 25 percent mortality (three times that of the general population). The prognosis was distinctly worse in women than in men chiefly because of a higher (45 percent) early mortality rate in women. Patients with recognized and unrecognized myocardial infarctions had similar survival rates after 3 years. A second myocardial infarction occurred in 13 percent of the men and in 40 percent of the women within 5 years of the first infarction. Thus, women were more prone to death and reinfarction than men. Congestive heart failure occurred as commonly as reinfarction, affliction 14 percent of the men within 5 years of the initial infarction. Once congestive failure ensued, half of the affected patients were dead within 5 years. Angina developed in one third of the patients within 5 years of their first infarction.