We report a 45 years old female with a HTLV-I associated myelopathy, followed up for 10 years who, five years ago, developed personality changes and intellectual deterioration, assessed with the Wais-Benton test. She also had alterations in the electroencephalogram and a nuclear magnetic resonance imaging of the brain showed hypodensity in T1 and hyperdensity in T2 subcortical regions. The progression of intellectual impairment was related to an increase in proviral DNA, assessed with polymerase chain reaction.