Mycosis Fungoides (MF) and Sézary syndrome (SS) are the most common forms of cutaneous T-cell lymphomas. Few validated prognostic factors have been reported in MF/SS, especially when compared with non-cutaneous lymphomas. Increased C-reactive protein (CRP) levels have recently been associated with poor clinical outcome in various malignancies. The aim of this study was to evaluate the prognostic significance of serum CRP levels at diagnosis in patients with MF/SS. This retrospective study included 76 patients with MF/SS. Stage was assigned according to the ISCL/EORTC guidelines. The follow-up period was 24 months or more. Disease course and response to treatment were determined using quantitative scales. Wilcoxon's rank test and multivariate regression analysis were used to analyze the data. Increased CRP levels correlated significantly with advanced stages (Wilcoxon's test, P>0.0001). Furthermore, increased CRP levels were associated with a lower treatment response rate (Wilcoxon's test, P=0.0012). Multivariate regression analysis showed that CRP is an independent predictor of advanced clinical stage at diagnosis.The present data suggest that elevated CRP levels could serve as a useful prognostic factor in MF/SS and may assist in guiding treatment choices.