The cornerstone in clinical evidence of the relative efficacy of thienopyridines (clopidogrel, ticlopidine) versus aspirin in the secondary prevention of vascular disease is the Clopidogrel versus Aspirin in Patients at Risk of Ischaemic Events trial. This trial showed a modest benefit in the reduction of vascular events by clopidogrel. The results differed according to qualifying disorder: myocardial infarction, -3.7%; ischaemic stroke, +7.3%; and peripheral arterial disease, +23.8% (P = 0.042). Similar results were found for ticlopidine after brain ischaemia. The safety of clopidogrel appears to be similar to that of aspirin and better than that of ticlopidine. However, the recent report of thrombotic thrombocytopenic purpura in association with clopidogrel causes concern.