At the present time, atherosclerosis of the major extracranial arteries to the brain is considered the cause of most strokes. Early intervention and stroke prevention utilized anti-coagulants such as coumadin and heparin. Results were largely equivocal due to the diverse nature of the underlying pathogenesis and due to problems that offset potential benefit. Emphasis gradually switched to aspirin and to other platelet anti-aggregant drugs because of mounting evidence that micro-emboli were a major element in transient ischemic attacks. Several studies have examined the potential benefit of aspirin in stroke prevention. The exact dose of aspirin that was maximally beneficial with minimal side effects was not completely established. There was evidence that low dose aspirin was as effective as higher doses. The American College of Chest Physicians (ACCP) made recommendations that if aspirin were issued as a primary anti-thrombotic agent, the dose should be 325 mg daily, except in patients with cerebrovascular disease in whom the lowest beneficial dose appeared to be one gram per day. The ACCP also pointed out that the risk of bleeding was substantially greater in patients with ischemic cerebrovascular disease and venous thromboembolism than in other high risk groups requiring anticoagulation. It advised that anticoagulant therapy was not needed, but that aspirin might be given at 325 mg per day.