The authors have presented case-reports of two patients with relapsing/remitting multiple sclerosis (MS) whose diagnosis of laboratory supported definite MS (Poser’s criteria) was established about three years before the appearance of intracranial tumors. Both patients were given immunomodulating (IFNbeta-1a, Avonex) and immunosuppresive therapy for a period of various duration. In the case of a 42-year-old man, the course of MS was complicated with a multifocal tumor in the suprasellar region and in the left cerebral hemisphere, confirmed by histology as an astrocytoma, resulting in the patient’s death. In the other case of a 25-year-old man, there was demonstrated an extensive cystic expansive process of mesencephalon with a tri-ventricular hydrocephalus. Only ventriculoperitoneal drainage was carried out without histological verification of a tumorous formation. Besides a primary brain neuroplasm, the possibility of metastatic affection (mixed germ cell tumor) revealed together with the intracranial expansion is not eliminated in this patient. The co-morbidity of MS and malignant brain tumors is relatively rare, but not exceptional. A causal relationship between the two disorders has not been proved so far.

        Key words: co-morbidity, multiple sclerosis, malignant brain tumors, interferon beta, immunosuppression