Various doses of aspirin have been shown to be effective in preventing thrombosis or vascular occlusion in several clinical conditions. Short-term studies have documented the efficacy of aspirin in preventing occlusion of saphenous vein bypass grants, preventing myocardial infarction in patients with unstable angina, preventing transient ischemic attacks and stroke in men with cerebral vascular disease, preventing occlusion of injured coronary arteries following transluminal angioplasty and aiding in reducing myocardial infarction and total mortality in patients receiving fibrinolytic therapy. Additionally, aspirin has been effective in the secondary prevention of myocardial infarction in subjects with known coronary artery disease. The results of the Physicians' Health Study, a large-scale primary prevention trial of aspirin in male physicians, have shown a decrease in myocardial infarction, a non-significant increase in cerebral vascular events, and no difference in overall mortality. However, few studies have addressed the efficacy of aspirin in vascular diseases in women, and it is possible that the risk to benefit ratio may be different in women. Specifically, there have been no large primary prevention trials in women, who are at risk of coronary heart disease, especially after menopause.