BACKGROUND: The introduction of the new TNM staging system for thymic epithelial malignancies produced a significant increase in the proportion of patients with stage I disease. The identification of new prognostic factors could help to select patients for adjuvant therapies based on their risk of recurrence. Neutrophil-to-lymphocyte ratio (NLR) has recently gained popularity as reliable prognostic biomarker in many different solid tumors. The aim of this study is to assess the utility of NLR evaluation as a prognostic marker in patients with surgically-treated thymoma. METHODS: A retrospective analysis was conducted among patients who underwent resection for thymoma in a single center. Patients were divided in two groups, under (low-NLR-Group = 47 patients, 60%) and above (high-NLR-Group = 32 patients, 40%) a ROC-derived NLR cut-off (2.27). Associations with clinical-pathological variables were analyzed; disease-free survival (DFS) was identified as the primary endpoint. RESULTS: Between 2007 and 2017, 79 patients had surgery for thymoma. Overall 5-year DFS was 80%. Univariate survival analysis demonstrated that NLR was significantly related to DFS when patients were stratified for TNM stage (p = 0.043). Five-year DFS in the low-NLR-Group and in the high-NLR-Group were respectively 100 and 84% in stage I-II, and 66 and 0% in stage III. TNM stage resulted as the only independent prognostic factor at multivariate analysis, with hazard ratio of 3.986 (95% CI 1.644-9.665, p = 0.002). CONCLUSIONS: High preoperative NLR seems to be associated to a shorter DFS in patients submitted to surgery for thymoma and stratified for TNM stage.