HTLV-I infection represents a major health concern in endemic areas throughout the world, such as Salvador, the main city of Bahia State, with socio-demographic characteristics similar to sub-Saharan African cities, located in the Northeast of Brazil. In order to provide an estimate of the frequency distribution, and range of neurological manifestations potentially related to HTLV-I infection in this city, we conducted a cross-sectional clinical–epidemiological study to determine the prevalence of this infection in patients with neurological diseases. Patients exhibiting vascular diseases, tumoral diseases or trauma were excluded. Over a period of 16 months, we studied 322 consecutive patients with chronic neurological diseases, who attended the neurological clinics of two major hospitals in Salvador. Overall, the prevalence of HTLV-I infection among the patients was 20.9% (67/320). However, the prevalence among the 104 patients with chronic myelopathy was 50.0% (52/104). It was observed that the major prevalence of HTLV-I was between the ages of 40 and 60 years with a female predominance. Our data indicate that, in Salvador city, HTLV-I is associated with chronic myelopathies or myeloneuropathies, which seem to be the only neurological diseases associated with HTLV-I.