Unless there are contraindications to the use of aspirin, aspirin should be used to treat patients with acute myocardial infarction (MI) and continued indefinitely to decrease vascular death, nonfatal MI, and nonfatal stroke. Clopidogrel added to aspirin is beneficial in the treatment of patients with acute ST-elevation MI. Patients with unstable angina pectoris or non-ST-elevation MI should be treated with aspirin plus clopidogrel for at least 9 mo to decrease vascular death, nonfatal MI, and nonfatal stroke. Patients with prior MI should be treated indefinitely with aspirin and with clopidogrel if aspirin is contraindicated. Patients with ischemic stroke should be treated with either aspirin or clopidogrel indefinitely. Clopidogrel is significantly more effective than aspirin in reducing vascular death, nonfatal MI, and nonfatal stroke in patients with peripheral arterial disease.