Background: A high proportion of patients with ST-segment elevation myocardial infarction (STEMI) visit emergency room more than 12 hour after symptom onset. In this setting, the chance of an existing coronary collateral circulation, the ischemic preconditioning and the infarct-related artery patency should be taken into consideration for patients with STEMI presenting from 12 to 72 h after symptom onset. These patients are known as 'early' latecomers. The aim of this study is to evaluate the benefit of primary percutaneous coronary intervention (PCI) in ���early��� latecomers with STEMI in modern PCI era. Methods: Between November 2005 and January 2008, 754 ���early��� latecomers (499 men; mean age = 65.2 짹 12.8 years-old) were analyzed from the Korean Acute MI registry. Patients were stratified into three groups based on symptom-to-door (STD) time; STD time of 12 - <24 hours (n = 369, 62.1%), 24 - <48 hours (n = 168, 28.3%), and 48 – 72 hours (n = 57, 9.6%). The 12-month MACE was defined as a composite of death, non-fatal MI, and revascularizations. Results: Of these patients, primary PCI was performed in 594 (78.8%) ���early��� latecomers. During the follow-up, 126 (16.7%) MACEs occurred. Kaplan-Meier survival curve showed primary PCI significantly reduced 12-month MACEs (21.4% versus 36.5%, Log-rank p <0.001) compared with conservative treatment group in overall ���early��� latecomers. There were no significant differences in 12-month MACEs (20.6% versus 21.8%, p = 0.772) between door-to-balloon (D2B) time of < 90min and D2B time ���90 minutes in primary PCI group. In Cox proportional hazards model, primary PCI (hazard ratio [HR] 0.604, 95% confidence interval [CI] 0.372 to 0.980, p=0.041) was an independent predictor of 12-month MACEs after adjustment for confounding variables. In subgroup analysis, 12-month MACEs were significantly lower in primary PCI group compared with conservative treatment group in patients with an STD time of 12 - <24hours (20.0% versus 37.0%, p = 0.007) and an STD time of 24 - <48 hours (19.0% versus 36.1%, p = 0.033). However, there were no significant differences in 12-month MACEs between primary PCI and conservative treatment in patients with an STD time of 12 - <24 hours (38.9% versus 35.7%, p = 0.836). Conclusions: The 'early' latecomers with STEMI represent a heterogenous group, many of these patients may derive significant benefit from immediate PCI.