Background/aim: The aim of the study was to evaluate the effect of Controlling Nutritional Status (CONUT) score on the prognosis in patients with diffuse large B-cell lymphoma (DLBCL). Materials and methods: The present study was a retrospective study. The CONUT score was calculated based on serum albumin, total cholesterol and lymphocyte levels. This study included a total of 266 patients, 131 (49.2%) were female and 135 (50.8%) were male. The median follow-up period was 51 months (range: 1-190). Results: The median age was 64 years. The cut off CONUT was 1.5. There was a significant difference between patients with high (>_ 2) or low (< 2) CONUT scores in terms of overall survival (OS) and progression-free survival (PFS). The 5-year OS and PFS in patients with high CONUT score was 52.1% and 49.7%. The 5-year OS and PFS in patients with low CONUT score was 79.8% and 75.6% (p < 0.001). In the multivariate analysis for OS, age >_ 65 years (HR = 1.80, p = 0.028), Eastern Cooperative Oncology Group (ECOG) > 1 (HR = 2.04, p = 0.006), stage IIIA-IVB disease (HR = 2.75, p = 0.001) and the CONUT score (HR = 1.15, p = 0.003) were found statistically significant. In the multivariate analysis for PFS, age >_ 65 years (HR = 2.02, p = 0.007), stage IIIA-IVB disease (HR = 2.42, p = 0.002) and the CONUT score (HR = 1.19, p = 0.001) were found to be significant parameters. Conclusion: High CONUT score reduces OS and PFS in DLBCL. CONUT score is an independent, strong prognostic index in patients with DLBCL.