Aim Early diagnosis and treatment is very important in acute coronary syndromes (ACS). Previous studies showed that not all non-ST elevation myocardial infarction (NSTEMI) patients should be considered and treated in the same way. The systemic immune-inflammation index (SII), which is an easily accessible, rapidly computed, and cost-effective parameter, was evaluated in this study to determine the optimal intervention time for NSTEMI.Material and methods 469 patients diagnosed with ACS were included to the study. STEMI and NSTEMI patients were compared according to their SII. Univariate and binary logistic regression analysis were performed to determine which parameters have a significant effect on the discrimination of types of myocardial infarction.Results The mean age of the patients was 61.43±11.52 yrs, and 348 (74.2 %) were male. NSTEMI patients with an SII value higher than 768×109 / l may be assumed to be STEMI (p<0.001). Univariate analysis and binary logistic regression showed that only SII and hypertension had statistically impact on differentiation of STEMI and NSTEMI. In addition, SII value of 1105×109 / l was the cut-off point for discrimination of cardiovascular survival (p<0.001, AUC =0.741). This study was performed to find out which NSTEMI patients should be treated percutaneously immediately after first medical contact according to SII. It was found that, SII value of higher than 768×109 / l is related with STEMI.Conclusion In conclusion, NSTEMI patients with a SII value higher than 768×109 / l may be considered as STEMI and treated with in 120 min after first contact. In addition, SII was found to be a cardiovascular mortality predictor after myocardial infarction, and this may be used for identifying high-risk patients after percutaneous coronary intervention.