OBJECTIVE To investigate clinical utility of on-site measurement of aspirin resistance in patients undergoing percutaneous coronary intervention (PCI) with drug-eluting stents (DES). BACKGROUND Data on long-term prognostic value of aspirin resistance in large number of ���real-practice��� patients receiving PCI with DES are limited. METHODS We prospectively evaluated 2849 patients who received DES and had VerifyNow aspirin assay measured at 24 to 48 hours post-PCI. Aspirin resistance was defined as an aspirin reaction units (ARU) > 550. The primary end point was a composite of all-cause death, nonfatal myocardial infarction, stent thrombosis, and stroke. RESULTS At post-procedure, overall incidence of aspirin resistance was 7.1% (203 patients). During follow-up of 2.2 years (median), the occurrence of the primary end point significantly higher in patients with aspirin resistance than those without aspirin resistance (5.4% vs. 1.9% at 2 year; log-rank P value = 0.004). After multivariable adjustment using Cox-proportional hazard regression analysis, aspirin resistance was significantly associated with a higher risk of primary endpoint (hazard ratio 1.91, 95% confidence interval, 1.35-3.88; P=0.035). There was no significant interaction between aspirin resistance measured by ARU and clopidogrel resistance measured by P2Y12 reaction units (PRU). CONCLUSION In this large number of ���real-world��� PCI patients treated with DES, aspirin resistance, measured by VerifyNow aspirin assay, was independently associated with long-term atherothrombotic risks.