The human T-cell lymphotropic virus type 1 (HTLV-1) associated myelopathy/tropical spastic paraparesis (HAM/TSP) diagnosis is based on the clinical signs and confirmation of HTLV-1 infection in the CNS. Electrophysiological tests may facilitate earlier diagnosis of spinal cord involvement. Vestibular evoked myogenic potential (VEMP) tests the vestibule-spinal tract, which is correlated with the motor tract, the target for damage in HAM/TSP. The aim of the study was to follow subclinical neurological alterations related to HTLV-1 infection in individuals with asymptomatic HTLV-1 infection, possible HAM/TSP, and HAM/TSP. VEMP was performed at the beginning of the follow-up and repeated every 6 months during a 2-year period. We selected 30 HTLV-1-seronegatives and 60 HTLV-1-seropositives. VEMP response was classified as normal or abnormal. The changing VEMP response from normal to abnormal was the event of interest. For this survival analysis, subjects with a normal VEMP during the first assessment were selected. The analysis of the results was conducted in a masked manner. VEMP stimulation included short tone bursts (1 kHz, 118 dBNA); the stimulation rate was 5 Hz; and it averaged 200 responses each run. The survival curve analysis indicated that the median time was over 18 months but was near 18 months for the HAM/TSP group (p = 0.022). In conclusion, the vestibulospinal tract is damaged earlier with an HTLV-1 infection; even clinical alteration does not show involvement. The changing VEMP results from normal to altered precede the clinical alterations with HTLV-1 neurological involvement and may be useful with HTLV-1 follow-up and HAM/TSP evolution.