In its classical meaning multiple sclerosis (MS) denotes a demyelinating disease of the central nervous system, resulting in a multifocal, multistage and, less frequently, chronic progressive neurological syndrome. Currently, MS is treated largely as a generalised degenerative disease of the brain and spiral cord, in which an inflammatory process leads to not only demyelination and injury of axons but also to loss of neurons and cerebral atrophy. In its anatomical patterns at the beginning a subacute inflammatory process prevails, which becomes transformed into a chronic inflammation, linked to manifestation of foci (plaques) of variable numbers, size and distribution. The lesions may be observed using magnetic resonance tomography in T1- and T2-dependent patterns. The methods demonstrate also atrophy of the grey matter, particularly within the cerebral cortex, which is of a high clinical significance, determining several signs/symptoms of the disease. Several morphological, mainly immunohistochemical studies, demonstrated extensive lesions not only to the myelin but also to axons, already in fresh lesions. In the cellular infiltrates numerous lymphocytes T and B are encountered, of a high significance for the immunological pathomechanism of the disease. Several data indicate that the pathological process in MS reflects to a significant extent apoptosis, particularly apoptosis of oligodendroglia cells. Neuropathological investigations, performed largely on peripheral blood lymphocytes suggest that a retrovirus associated with MS may play a role in aetiology of MS. The extensive discussion whether MS is a uniform nosological unit still continues and, until now, only certain variability of neuropathological lesions, mainly demyelination, has been proven.