Background Primary percutaneous coronary interventions (PCI) have been proposed as a novel superior management strategy in patients with ST elevation myocardial infarction (STEMI). This study tested the hypothesis that in the acute phase of myocardial infarction with ST-segment elevation, the neutrophil/lymphocyte (N/L) ratio is a predictor of long-term prognosis.Methods We analyzed 551 consecutive STEMI patients treated with primary PCl at a single university center. Patients were stratified according to quartiles of the mean neutrophil/lymphocyte ratio.Results Kaplan-Meier survival analysis showed a cumulative eight-year survival of 94.2% in the first quartile, 92.0% in the second quartile, 91.3% in the third quartile, and 75.4% in the fourth quartile (P ＜0.001 by log rank). Relative to patients in the other three lower N/L ratio quartiles, patients in the highest quartile were more than four times more likely to die during hospitalization (P ＜0.001) and during long-term follow-up (P ＜0.001). By multivariate Cox regression analysis including baseline demographic, clinical, and angiographic covariables, the N/L ratio in the highest quartile remained an independent predictor of mortality (hazard ratio 2.38, 95% confidence interval (CI) 1.42 to 3.98; P=0.001).Conclusion The neutrophil/lymphocyte ratio is a strong independent predictor of long-term mortality after ST elevation myocardial infarction treated with very early revascularization.