Background : An early invasive strategy using percutaneous coronary intervention (PCI) is currently the recommended treatment for patients at high risk for acute non-ST segment elevation myocardial infarction (NSTEMI). However, information on early intervention is limited in Korea. We analyzed the prognosis according to the timing of PCI in patients with acute NSTEMI enrolled in the KAMIR. Methods : Among the patients enrolled in the KAMIR, we studied 1,141 patients at high risk for acute NSTEMI. We stratified them by the time interval from the onset of chest pain to the PCI (Group I < 24 hr, Group II 24-48 hr, Group III > 48hr). The clinical outcomes were evaluated based on major adverse cardiac events (MACE) at 1 and 6 months follow up. Results : The baseline characteristics were similar in the three groups. There was no significant differences in the 1 and 6 month MACE (p=0.762, p=0.279). The incidence of MACE at 6 months was 5.1% in Group I, 6.3% in Group II and 8.5% in Group III. The early PCI groups showed a low incidence of MACE at 6 months; however, this difference was not statistically significant (p=0.279). Conclusion : In patients at high risk for acute NSTEMI, the incidence of MACE at 6 months was lower when PCI was performed early. However, the results were not statistically significant. Therefore, early PCI should be considered in high risk patients with acute NSTEMI.