Antiplatelet therapy (chiefly aspirine alone) greatly reduces the risk of vascular death and vascular events in patients with acute myocardial infarction, past history of myocardial infarction, unstable angina, stroke or transient ischaemic attack, and also in the large categories of patients at increased risk of occlusive vascular diseases. Studies of patients with peripheral arteriopathy demonstrate that antiplatelet therapy significantly reduces the risk of vascular occlusions in patients with intermittent claudication or with saphenous vein grafts or prosthetic implants or angioplasty for lower limb diseases. In trials in high risk patients where patients data were available, antiplatelet therapy produces a similar effect in middle age or old age, in men or women, in diabetic and non-diabetic or in hypertensive or normotensive patients. There is no clear evidence that antiplatelet therapy is indicated in primary prevention. Medium dose aspirin (75-325 mg/d), probably for indefinite continuation, is the most widely tested antiplatelet regimen.