Data from 30 years of follow-up of the original Framingham Study cohort of 5,070 men and women aged 30-62 years who were first examined during the period 1948-1952 and who were free of cardiovascular disease reveal that blood pressure is a strong and consistent predictor of the development of coronary heart disease, stroke, transient ischemic attack, and congestive heart failure. Other factors related to blood pressure like obesity, left ventricular hypertrophy as demonstrated on electrocardiograms, and heart enlargement as shown by x-ray radiography made several selective additional independent contributions to risk; heart enlargement by x-ray radiography was the best predictor of congestive heart failure.