The paper presents the results of immunohistochemical study of tenascin expression in 62 specimens of cerebellar medulloblastomas. All tumors can be classified as belonging to one of the 3 types of immunoreactivity: (1) tenascin-negative medulloblastomas, (2) tumors with extracellular and (3) intracellular expression of tenascin. Immunoreactivity was demonstrated in 61% of specimens. It perfectly matches the incidence of metastases. Medulloblastomas with intracellular tenascin expression demonstrated higher proliferative potential and are capable of expressing other oncoproteins (i.e. p 53, bcl-2). The data obtained in the study brought us to the conclusion that in patients with positive tenascin expression the prognosis is worse.