Lower limb somatosensory evoked potentials (LSEPs) were performed along with neurological evaluation in 96 HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients. The N20 latencies were abnormal in 5 cases. Central sensory conduction time (CSCT) was abnormal in 42 cases. A highly significant correlation (p < 0.001, r = 0.418) was found between CSCT and disability score. Such a correlation was not found between CSCT and other clinical findings, onset of illness, illness duration, serum and CSF antibody titer to HTLV-I and vibratory sensation. There was no difference of the mean of CSCT between the cases with sensory impairment and those without it. This shows that LSEPs are useful to estimate the disability of HAM/TSP. Also the cases with delayed CSCT and normal sensation suggest that LSEPs are capable of detecting subclinical lesions of the spinal cord in HAM/TSP.