Background : Intravascular ultrasound (IVUS) guided percutaneous coronary intervention (PCI) was useful in optimal stent deployment. The aim of this study was to assess the impact on clinical outcome and safety in IVUS-guidance PCI with drug-eluting stents (DES). Methods: A total of 733 AMI patients (65.0 짹 12.8 years, 71.9% males) enrolled in a nationwide prospective Korea Working Group on Myocardial Infarction (KorMI) between Feb. 2008 and Jul. 2009. All of them had completed one-year clinical follow-up. The study patients were divided into two groups as follows: group I (IVUS guided PCI, n=175) and group II (Not IVUS-guided, n=558). The primary end point was a major adverse cardiac events (MACE), composite of all cause of death, myocardial infarction (MI) and Re-PCI (target lesion or vessel revascularization). Definite or probable stent thrombosis according to Academic Research Consortium (ARC) definition at 12 months was the secondary end point of this study. Results: During the one-year follow-up, the primary end point occurred in 181 patients (24.7%). Stent thrombosis was occurred 17 patients (2.3%) at one year. In-hospital mortality (15.4% vs. 15.1%, p=0.904) and complication rate (19.4% vs. 16.7%, p=0.592) were similar in both groups. ST-segment elevation myocardial infarction (STEMI) was diagnosed in 102 (58.3%), 338 (61.7%) patients each group (p=0.42). There were no significant differences between two groups in baseline characteristics such as age, gender and the prevalence of coronary artery disease risk factors. In terms of procedural factors, the incidence of multi-vessel disease (58.3% vs. 57.7%, p=0.892), B2/C lesion (80.3% vs. 79.8%, p=0.889), ejection fraction below 40% (15.3% vs. 16.9%, p=0.650) and Thrombolysis In Myocardial Infarction (TIMI) flow (��� III) after procedure (3.6% vs. 4.7%, p=0.573) were similar in two groups. IVUS-guided PCI group, however, tended to longer stent size (26.0짹6.84 mm vs. 24.9짹6.96 mm, p=0.078), more left main disease (10.9% vs. 3.8%, p<0.001), less using glycoprotein IIb/IIIa inhibitor (18.3% vs. 21.1%, p=0.015) and more number of stent implantation (1.8짹1.0 vs. 1.5짹0.8, p<0.001). On multivariate Cox regression analysis, which adjusted with all parameters as mentioned above, IVUS-guided PCI did not reduce the MACE (death, MI, Re-PCI) rate [Hazard ratio (HR) 1.28, 95% confidential interval (CI) 0.72-2.26, p=0.218], stent thrombosis (HR 0.755, 95% CI 0.16-3.47, p=0.718) and death or MI (HR 1.403, 95% CI 0.72-2.73, p=0.318) at one year. Conclusion: IVUS-guided PCI has no long-term clinical improvement in point of reducing MACE, stent thrombosis in our study. It needs further study for longer duration.