Background: Primary PCI (percutaneous coronary intervention) is recommended for patients with the clinical manifestation of STEMI (ST-segment elevation myocardial infarction) within 12 h after symptom onset and with persistent ST-segment elevation. However, there is no consensus as to whether primary PCI is effective in late comers who visit emergency room after 12 hours from symptom onset. Methods: In our retrospective study, 1458 patient was enrolled as late comer STEMI patient. According to therapeutic strategy, the patients was classified into two group.( Group A: PCI group, n=1336 vs Group B: medical therapy group, n=120). And we divided late-comers according to symptom-to-door time(SDT) into group I(12< SDT< 24), group II ( 24 < SDT< 36), and group III (36 < SDT). The clinical outcome of each group was compared. Primary endpoint is in-hospital survival and major adverse cardiovascular event (MACE) after1, 6, 12 months in group A and group B. The secondary end point is in-hospital survival rate of group I, group II and group III after PCI. The data was registered at KORMI(Korean Working Group on Myocardial Infarction). Results: The late-comers who underwent primary PCI has better in-hospital survival outcome than medical therapy group (1280 (92%) in group A vs. 100 (83%) in group B, p=0.007). However, MACE rate after 1, 6, 12 months was not different statistically between two group (MACE after 1 month; p=0.621, MACE after 6 months; p=0.083, MACE after 12 months; p=0.380). The in-hospital survival rate of group I, group II and group III after PCI( Group I; n=421, survival rate=93%, Group II; n=207, survival rate=91%, Group III; n=708, survival rate=92%) was not statistically different( G1 vs G2; p=0.283, G2 vs G3; p=0.574, G1 vs G3; p=0.427). Conclusions: Although long-term MACE was not affected by treatment strategy, in-hospital survival rate of late comers was better in PCI group than in medical therapy group. Long-term clinical outcome would be determined by other factors. And for late-comers, urgent PCI is not necessary.