Backgrounds: While cytochrome P450 2C19 (CYP2C19) reduced-function polymorphism has been reported to adversely affect long-term clinical outcomes in patients with acute myocardial infarction (MI) treated with drug-eluting stents (DES) and on clopidogrel, the impact of CYP2C19 *2 or *3 genotypes on clinical efficacy of clopidogrel in patients who received elective percutaneous coronary intervention (PCI) are lacking. Thus the aim of this study was to assess the impact of CYP2C19 reduced-function polymorphisms on clinical outcomes in clopidogrel-treated patients undergoing elective PCI. Methods and Results: The study population included 2000 patients undergoing elective PCI with DES after excluding patients with acute MI. Genotyping is under way using Multiplex SNaPshot assay for CYP2C19, CYP2B6, CYP3A4, and CYP3A5, and now available in 472 patients. All patients underwent VerifyNow P2Y12 system for platelet response to clopidogrel. Primary efficacy outcome was composite of cardiac death or MI during 3-year clinical follow up. The prevalence of carriers of reduced-function allele of each gene was 60 % in CYP2C19, 27.1 % in CYP2B6, 0% in CYP3A4, and 60.4 % in CYP3A5. The baseline characteristics were similar between carriers and non-carriers of reduced-function allele of CYP2C19. The value of P2Y12 reaction units (PRUs) was higher in carriers (248 vs. 212, p=0.024). However, there were no differences in the primary efficacy outcome (carrier vs. noncarrier 4.2 % vs. 3.2 %, p=0.554, figure) Furthermore, no differences were found in the incidences of all-cause death, cardiac death, MI, or stroke between two groups (2.5 % vs. 2.2 %, p=1.0, 2.5 % vs. 2.9 %, p=1.0, 2.0 % vs. 1.5 %, p=1.0, 0.5 % vs. 0.7 %, p=1.0, 2.0 % vs. 3.7 %, p=0.493, 6.9 % vs. 3.7 %, respectively). Conclusions: While the prevalence of carriers is higher in Korean (60%), the CYP2C19 reduce-function genotypes is not associated with adverse clinical outcomes in angina patients undergoing elective PCI. Ongoing genotyping of the remaining patients will be presented on October.