Aim: Acute aortic dissection is a life-threatening cardiovascular emergency. Neutrophil-to-lymphocyte ratio is proposed as a prognostic marker and found to be related to worse clinical outcomes in various cardiovascular diseases. Te aim of the present study was to evaluate the relationship between admission neutrophil-to-lymphocyte ratio and in-hospital mortality in acute type I aortic dissection. Materials and methods: We retrospectively evaluated 123 consecutive patients who had undergone emergent surgery for acute type I aortic dissection. Patients were divided into 2 groups as patients dying in the hospital (Group 1) and those discharged alive (Group 2). All parameters, including neutrophil-to-lymphocyte ratio, were compared between the 2 groups and predictors of mortality was estimated by using multivariate analysis. Results: A total of 104 patients (79 males, mean age: 55.2 ± 14 years) were included in the fnal analysis. In multivariate analyses, cross-clamp time, cardiopulmonary bypass time, intensive care unit duration, platelet count, and neutrophil-to-lymphocyte ratio were found to be independent predictors of mortality. Patients with higher neutrophil-to-lymphocyte ratios had a signifcantly higher mortality rate (hazard ratio: 1.05; 95% CI: 1.01-1.10; P = 0.033). Receiver operating characteristic analysis revealed that using a cut-of point of 8, neutrophil-to-lymphocyte ratio predicts mortality with a sensitivity of 70% and specifcity of 53%. Conclusion: Tis study suggests that admission neutrophil-to-lymphocyte ratio is a potential predictive parameter for determining the in-hospital mortality of acute type I aortic dissection. © TÜBİTAK.