A case of multiple sclerosis (MS) occurred in which there were recent demyelinated plaques in the CNS, and inflammatory demyelination and remyelination in the peripheral (Schwann cell) portions of the spinal roots. The lesions in the peripheral nervous system (PNS) were characterized by inflammation, primary segmental demyelination, myelin stripping, the occurrence of lipid debris-containing macrophages in the endoneurium, and remyelination. To our knowledge, this is the first description of simultaneous acute inflammatory demyelination in the CNS and PNS in MS.