Tropical spastic paraparesis (TSP) is a common myeloneuropathy with primary and predominant involvement of the pyramidal tract and minimal sensory loss. The epidemic form of TSP is related to toxic nutritional factors, but the endemic form occurs in clusters in tropical areas, especially in India, Africa, the Seychelles, Colombia, and areas of the Caribbean. We describe the clinical and epidemiological features of 25 TSP patients from Martinique (French West Indies) with serum antibodies to human T-lymphotropic virus type I (HTLV-I). Furthermore, all 11 patients who were seropositive for HTLV-I had specific HTLV-I antibodies in their CSF. All were women. The age of onset varied from 25 to 60 years (mean, 45 years). The main clinical features are spastic paraparesis or paraplegia with spasticity of the upper limbs, minimal sensory loss, and bladder dysfunction. Minimal estimated incidence and prevalence are 1 per 100,000 inhabitants per year and 8 per 100,000, respectively. Seventeen percent of the relatives of patients with HTLV-I-associated TSP have HTLV-I antibodies (1 husband and 7 children). In Martinique, the prevalence of HTLV-I antibodies in the general population is about 2% and reaches 10% for neurological disorders other than TSP. Since our initial report, the association between spastic paraparesis and HTLV-I has been confirmed in Jamaica, Colombia, and Japan, suggesting the neurotropism of this lymphotropic human retrovirus.