Background The benefit of statin use after acute ST-segment elevation myocardial infarction (STEMI) has been well established, however, the influence of the timing of statin administration has not been elucidated. The objective of this study focused on early clinical outcomes after percutaneous coronary intervention (PCI). Methods This analysis of the Korea Working Group on Myocardial Infarction registry (KorMI) study included 3,584 STEMI patients (mean age, 63 ±13 years;male, 2,684, 74.9%) undergoing PCI from January 2008 to June 2009. Rates of major adverse cardiac events (MACE:all-cause death, recurrent MI, and target lesion revascularization) were compared among patients grouped according to statin therapy timing:I, both during and after hospitalization (n=2,653, 74%);II, only during hospita-lization (n=309, 8.6%);III, only after discharge (n=157, 4.4%);and IV, no statin therapy (n=465, 13%). Mean follow-up duration was 234 ± 113 days. Results Multivariate factors of statin use during hospitalization included prior statin use, multiple diseased vessels, final thrombolysis in myocardial infarction flow grade III, and low-density lipoprotein cholesterol level. At 6-month follow-up, groups III and IV had the highest MACE rates (2.3%, 3.9%, 5.1%, and 4.9%for groups I-IV, respectively, P=0.004). After adjusting for confounders, groups II-IV had a higher MACE risk than group I [hazard ratio (HR):3.20, 95%confidence interval (95%CI):1.31-7.86, P=0.011;HR:3.84, 95%CI:1.47-10.02, P=0.006;and HR:3.17, 95%CI:1.59-6.40, P=0.001;respectively]. Conclusions This study, based on the national registry database, shows early and continuous statin therapy improvs early outcomes of STEMI patients after PCI in real-world clinical prac-tice.