The case of a young female patient with acute symmetrical ascending polyneuropathy as a manifestation of systemic lupus erythematosus is reported. There was involvement of several cranial nerves and the cerebrospinal fluid showed albuminocytologic dissociation. Pathologic examination of the sural nerve showed degeneration of myelinated fibers, fibrosis of the perineurium and endoneurium, and overgrowth of the medial layer of the vasa-nervorum. The authors call atention to the uncommonn involvement of the peripheral nervous system in S.L.E. They believe that a abnormal autoimune reaction could be responsable for the nerve fiber degeneration.