Objectives: We aimed at comparing the clinical outcomes of the patients who underwent percutaneous coronary intervention (PCI) for ST segment elevation myocardial infarction (STEMI) due to left main coronary arteries (LMCA) and non-LMCA determining the predictors of mortality in the patients. Background: There are few data regarding the midterm prognosis of STEMI due to LMCA as compared with them due to non-LMCA. Methods: A total of 4,697 patients with STEMI (61 patients with LMCA and 4,636 patients with non-LMCA) were enrolled in a nationwide Korea Acute Myocardial Infarction (MI) Registry between November 2005 and September 2009. The primary endpoints was a composite of cardiac death, nonfatal MI, and target lesion and vessel revascularization (TLR/TVR) during a 12-month clinical follow-up. Results: The LMCA group had a higher incidence of total major adverse cardiac events (MACEs) (26.2% vs. 7.8%; P < 0.001) at 12 months, which was largely attributable to cardiac deaths at 1 month (21.3% vs. 3.8%; P < 0.001). Therefore, there was no statistical difference in cardiac deaths, nonfatal MI, TLR/TVR, and MACEs after 1 month between the two groups. Presenting in cardiogenic shock (HR, 4.25; 95% CI, 1.01–17.97; P = 0.049) and heart rate ≥100 bpm (HR, 4.97; 95% CI, 1.18–21.00; P = 0.029) were independent predictors of cardiac death due to LMCA. Conclusion: Patients with STEMI and a LMCA had poor clinical outcomes, which is attributable to hemodynamic deterioration during the periprocedural period. However, after that time, midterm MACEs of the survivors following the periprocedural period may not be different between STEMI due to LMCA and non-LMCA. © 2011 Wiley Periodicals, Inc.