Using non-invasive brachial artery ultrasound, endothelial function was examined in about 3,800 men and women of the Framingham Heart Study. The cross-sectional correlates of endothelial function with known coronary risk factors were examined and cross-sectional analyses were performed on the relation of endothelial function to prevalent cardiovascular disease. Observations were made of the adjusted relation of endothelial function to incident and recurrent cardiovascular events. The central hypothesis was that the presence of endothelial dysfunction was an independent risk factor for cardiovascular disease events.