An autopsy case of human T lymphotropic virus I-associated myelopathy (HAM) of a duration of 28 years in a 61-year-old man with serological confirmation of HTLV-I infection was reported. The spinal cord was grossly atrophic. There was severe symmetrical degeneration of the lateral funiculi, particularly of the bilateral pyramidal tracts, involving all levels of the spinal cord, but anterior horn cells were relatively well preserved. In the most severely damaged middle and lower thoracic segments, the white matter degeneration also involved the anterior funiculi. In the degenerated white matter, both the myelin and axons were equally lost and had been replaced by glial scars. Marked adventitial fibrosis was commonly seen in small parenchymal vessels in both the white and gray matter. Although there was no evidence of inflammation in the spinal cord, mild lymphocytic infiltration was occasionally observed in the subarachnoid and perivascular spaces in the brain stem, cerebellum and cerebrum. This case was considered as a burnt-out case of HAM.