Cutaneous T-cell lymphomas (CTCLs) are slowly progressive diseases with a poor prognosis. There are no specific prognostic factors in development of cutaneous lymphomas. SATB1 protein controls expression of many genes, including the cellular cycle and apoptosis. The subject of our study was the expression of SATB1 protein in the skin sample in patients with mycosis fungoides and Sezary syndrome and its correlation with clinical course. Immunohistochemical reaction with SATB1 antibody was observed in 29 cases of mycosis fungoides of different stages (15 patients) and two cases of Sezary syndrome. SATB1 expression was observed in 22 cases of mycosis fungoides, 7 of which were in the patch stage, 11 were in the plaque stage and 4 were in the tumor stage. SATB1 expression was not found in 2 cases of the patch stage, 4 cases of the plaque stage and one case of the tumor stage. Negative reaction was confirmed in both cases of the Sezary syndrome. There were no changes in SATB1 expression during progression of the disease. A group of patients with the positive reaction of the SATB1 is characterized by a noticeably longer time to progression between the stages. The SATB1 expression seems to be a potential prognosis factor confirming the inner heterogeneous features of CTCLs.