Background: Aspirin is an effective antiplatelet agent with proven benefit in the prevention of atherothrombotic complications of cardiovascular disease. Aspirin resistance has been reported to occur in 5% to 45% of the general population in USA. We sought to investigate the prevalence of aspirin resistance in Korean population and the association with clinical events. Methods: We prospectively enrolled 146 patients (98 men, mean age 62짹12) scheduled for coronary angiography on aspirin and no other antiplatelet agents. We used the Ultegra Rapid Platelet Function Assay-ASA (VerifyNowTM Aspirin Assay, Accumetrics Inc. San Diego, California), approved by FDA, to determine aspirin resistance. Aspirin resistance based on the RPFA-ASA is defined as an ARU (aspirin reaction units) ��� 550 in a patient taking aspirin. The primary outcome was the composite of recurrent angina, MI, death, or CVA. Demographic information, laboratory data, and aspirin dosage were collected. Results Of the patients studied, the mean ARU was 480.8짹90.3, and by this study, 38 (26.0%) patients were aspirin resistant and 108 (74.2%) patients were not aspirin resistant. During follow-up (mean duration 52.6 days), aspirin resistance was associated with an increased risk of recurrent angina (7.9 % vs. 2.8 %, hazard ratio 3.09, p=0.04), but other clinical events didn���t occur in both groups. Conclusions: The prevalence of aspirin resistance is not low in Korean population. Further clinical follow-up are needed to correlate aspirin resistance to adverse clinical events.