In most cases the only manifestation of nervous system pathology associated with HTLV-1 infection is spastic paraplegia. The virus is transmitted by breast-feeding from mother to child, by transfusion of contaminated blood (or by syringes of intravenous drug addicts) or sexually from husband to wife. Paraplegia usually begins progressively after the age of 30 years by motor and sphincteral disorders, followed by a phase of stabilization. Other clinical entities, such as pseudo-LAS syndromes, polymyositis, lymphocytic alveolitis, vasculitis or meningitis, may coexist or show varying degrees of expression. There is no treatment capable of modifying the course of the disease, but corticosteroids are worth trying, notably in the initial stages of paraplegia and in polymyositis.