Progressive multifocal leukoencephalopathy (PML) is rare and very severe disease, classified into the group of subacute and viral infections of central nervous system (CNS), and can simulate clinical pictures of numerous degenerative diseases of nervous system. PML was firstly described in 1958, and pathologic-morphologic substrate was explained in papers of Astron et al. Many years later, definitive diagnosis of PML was histopathologic, on the autopsy material. The fact that it is very rare and severe disease, very rarely diagnosed in clinical conditions, is the reason of our decision to present this case.