Background: Primary percutaneous coronary intervention (PCI) was treatment of choice for acute ST elevation myocardial infarction (ASTEMI). The evidence of non-culprit revascularization at the time of primary PCI was not clear. We examined the incidence of and propensity for non-culprit interventions performed at the time of the primary PCI and its association with 1-year clinical outcomes. Methods: We examined the incidence and associated 1-year outcomes following non-culprit interventions performed at the time of primary PCI among STEMI patients with multi-vessel coronary artery disease (CAD). Between November 2005 and Aug 2007, 3,133 patients who underwent primary PCI were examined in the KAMIR database. The primary end-point was cardiac mortality and MACE(cardiac death, MI, TLR) during 1-year. Results: Of the 3,133 patients who underwent primary PCI in the KAMIR, 1,126 (35.9%) had multi-vessel CAD. Of those, 227 (20.2%) underwent infarct-related arteries (IRA) and non-infarct-related arteries (non-IRA) PCI, whereas 899 (79.8%) underwent PCI of the IRA alone. The 1-month, 6-month, 1-year mortality (1.4% in IRA and non-IRA group vs 0.6% in IRA only group, 1.4% vs 0.7%, 2.2% vs 2.5%, p=NS) and 1-month, 6-month, 1-year MACE (death, MI, revascularization) (1.3% in IRA and non-IRA group vs 2.7% in IRA only group, 3.1% vs 5.5%, 3.6% vs 3.5%) showed no significant difference between the two groups. Conclusion : Non-culprit coronary interventions were performed at the time of primary PCI in 20% of MVD patients and were showed no additional clinical benefits. This results support current guideline recommendations discouraging the performance of such procedures in stable primary PCI patients.