The recent CAPRIE trial (clopidogrel versus aspirin in patients at risk of ischaemic events) compared clopidogrel with aspirin in reducing the risk of vascular events in 19,185 patients with clinical manifestations of atherosclerosis. Participants were randomized to receive daily oral clopidogrel (75 mg) or aspirin (325 mg). Treatment periods ranged from 1 to 3 years. The primary outcome measurement was an aggregate of myocardial infarction, ischemic stroke and vascular death. Event rates of 5.32% and 5.83% were associated with clopidogrel and aspirin therapy, respectively. Clopidogrel therapy resulted in a relative risk reduction of 8.7% (CI 0.3-16.5%) compared with aspirin therapy (p = 0.043). Gastrointestinal hemorrhages occurred in 1.99% of patients treated with clopidogrel and 2.66% of patients treated with aspirin (p < 0.002). There were no significant treatment-based differences in the rates of intracerebral hemorrhages and hemorrhagic deaths or thrombocytopenia. These results indicate that clopidogrel is more effective and safer than aspirin in reducing adverse cardiovascular events in patients with atherosclerosis.