• Thirty-six patients with human T-cell lymphotropic virus type I (HTLV-I)—associated myelopathy were studied by electroencephalogram. Twenty-two of 36 patients showed mild to moderate electroencephalographic abnormalities, ranging from poor organization or slowing of the background activity to theta bursts and/ or spikes. None of these abnormalities were considered specific for HTLV-I—associated myelopathy. These electroencephalographic abnormalities had no apparent relationship to duration or severity of illness, nor to HTLV-I antibody titers in the cerebrospinal fluid. We document electroencephalographic changes in HTLV-I—associated myelopathy. Our data are consistent with previous reports describing the fact that involvement of regions above the spinal cord may exist in HTLV-I—associated myelopathy.