Background. The role of inflammation has been established in cancer biology and the neutrophil to lymphocyte ratio postulated as a marker of systemic inflammatory response. The prognostic significance of neutrophil to lymphocyte ratio has never been explored in patients with mycosis fungoides. Methods. Data from 119 mycosis fungoides (MF) patients, diagnosed between 1998 and 2015 at a single centre, were evaluated retrospectively. The prognostic influence of the neutrophil to lymphocyte ratio and other clinico-pathological factors including age, lactate dehydrogenase, stage of disease, beta-2-microglobulin levels, and total IgE levels were evaluated. Results. The mean value of absolute neutrophil count and absolute lymphocyte count (ANC/ALC) ratio was 2.07 +/- 1.17 in the patient group, whereas it was 1.76 +/- 0.53 in the control group (P<0.05). An ANC/ALC value of 2.85 corresponded to the maximum combined sensitivity and specificity on the ROC curve. ANC/ALC ratios of 2.85 or higher at diagnosis were positively correlated with elevated Beta-2-microglobulin (P=0.026), advanced disease stage, and disease progression (P=0.026, r=0.204) (P=0.006, r=0.251) (P=0.018, r=0.216). Conclusion. In the present study, we showed that a high ANC/ALC ratio at diagnosis of MF represents a simple, poor prognostic factor for identifying high-risk patients with MF.