Multiple sclerosis (MS) is one of the main chronic inflammatory diseases of the central nervous system that causes functional disability in young people. The aim of this study was to investigate the neutrophil-to-lymphocyte ratio (NLR) in patients with MS and the relationship between the NLR and the severity of the disease. One hundred and two MS patients (31 patients were in relapse; 71 patients were in remission) and 56 healthy controls were included. Complete blood counts as well as demographic and clinical data from MS patients were evaluated retrospectively. The NLRs were calculated for all participants and were compared; the cut-off value was also determined for the NLR and Expanded Disability Status Scale (EDSS). MS patients had a significantly higher NLR (p < 0.001) than the control group. The NLR levels were significantly higher in patients who were in relapse than patients in remission (p = 0.039). The cut-off value for the NLR to predict an MS diagnosis and activity were determined to be 2.04 and 3.90, respectively. The NLRs were directly correlated with erythrocyte sedimentation rate levels (r = 0.795, p < 0.001). Logistic regression analysis with dichotomous EDSS score showed that a high NLR was an independent predictor of the progression of disability. The NLR may be a biomarker that has simple, quick, inexpensive and reproducible properties in MS to predict patient's prognosis.