The human T-cell lymphotropic virus type 1 (HTLV-I) causes a neurological disease known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in a minority of infected individuals. Although other neurological outcomes have been described their prevalence is presently unknown. To evaluate the frequency and characteristics of neurological involvement in a population of HTLV-I-infected blood donors we investigated 196 HTLV-I positive and 196 negative blood donors from a blood center of Rio de Janeiro, Brazil. Individuals with abnormalities at the neurological examination were examined by three neurologists, and when pertinent, additional neurological investigations were performed. Descriptive analysis, Student's t-test and chi2 test were employed for statistical analysis. Neurological abnormalities were found in 71 (36.2%) of the HTLV-I positive blood donors and in only 29 (14.8%) of the HTLV-I negative donors (OR = 2.54, 95% CI = 1.67-3.59, p = 0.000002). Cases of myelopathy, motor neuron disease and myopathy were only found in the HTLV-I positive group. In addition, peripheral neuropathy (PN) was significantly more frequent in the positive group (p = 0.015). In summary, our data suggest that HTLV-I-infected individuals exhibit a wide variety of neurological manifestations apart from the classical picture of HAM/TSP.