Background: There are limited data regarding the prognosis of acute non-ST segment elevation myocardial infarction (NSTEMI) patients (pts) with Left main coronary artery (LMCA) disease as compared with those of pts with non left main disease patients. Methods: The study population consisted of 2,858 consecutive acute NSTEMI pts enrolled in the Korea Acute Myocardial Infarction Registry (KAMIR) study from November 2005 to June 2008. We compared the clinical outcomes of NSTEMI pts with LMCA disease (n=98, 3.43%) to those of pts with non- LMCA disease (n=1699, 59.4%) who underwent percutaneous coronary intervention (PCI). Results: The baseline clinical and procedural characteristics were balanced between pts with LMCA disease to those of pts with non- LMCA disease except higher number of elderly patients [(66.12짹 11.1) vs (63.2 짹11.8 ),p=0.016], higher number of prior history of MI [15 (15.3) vs 207 (7.5 ), p=0.011], higher usage of unfractionated heparin [72(73.5)% vs 1690 (61.2%), p=0.014] were noted in the left main group. At 12 month, although the major clinical outcomes including mortality and repeat PCI were similar between the two groups, there was a trend toward higher incidence of total major adverse cardiac events (MACE) in the LMCA group. Further, target lesion revascularization (TLR), any re-AMI and recurrent NSTEMI were significantly higher in pts with LMCA group after the multivariate analysis (Table). Conclusion: The prevalence of LMCA disease was in less proportion (3.43%) in the acute NSTEMI setting but showed worse one-year major clinical outcomes due to more TLR, cumulative recurrent NSTEMI in the LMCA disease group at one year.