Background: Higher neutrophil to lymphocyte ratio (NLR) has been associated with poor clinical outcomes in patients who have several cardiac diseases. However, the clinical availability of NLR in patients with STEMI undergoing primary PCI has not been known. The aim of this study was to evaluate the impact of NLR level on long-term clinical outcomes in patients with STEMI undergoing primary PCI with drug-eluting stents. Methods: We analyzed 326 consecutive STEMI patients treated with primary PCI within 12 hours of onset of symptom. White blood cells and differential count were measured at admission. Patients were divided into tertiles according to the level of NLR; NLR ���3.30 (Low group, n=108, 1.92 짹 0.84), 3.31< NLR ���6.52 (Medium group, n=108, 4.87 짹 0.94) and NLR >6.53 (High group, n =110, 11.86 짹 9.34). We sought major adverse cardiac events (MACE), composite of all cause of death, nonfatal myocardial infarction and ischemic stroke at a 12-month follow-up. Results: High NLR group was associated with a significantly higher rate of 12-month MACE (19.1% vs. 3.7%, p <0.001) and death (18.2% vs. 2.8%, p <0.001) compared to low NLR group. High NLR group was also associated with a significantly higher rate of in-hospital MACE (12.7% vs. 2.8%, p=0.010) and death (12.7% vs. 1.9%, p=0.003) compared to low group. In multivariable modeling, after adjusting for gender, left ventricular ejection fraction, creatinine clearance and factors included in TIMI risk score for STEMI, high NLR group (vs. low NLR group) was an independent and significant predictor of 12-month MACE (HR 3.33, 95% CI 1.09 to 10.16, p = 0.035) and death (HR 4.10, 95% CI 1.17-14.46, p=0.028). There was a significant gradient of 12-month MACE across tertiles of NLR with a markedly increased MACE hazard in those in high NLR group (log rank test p=0.002)(Figure). Conclusion: The NLR was a useful and powerful marker to predict a 12-month MACE in patients with STEMI who underwent primary PCI with drug-eluting stents.