Recent reports have demonstrated that human T lymphotropic virus type 1 (HTLV-1) is associated with other neurological abnormalities in addition to HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It has been well established that high HTLV-1 proviral loads are associated with the development of HAM/TSP. We now demonstrate, for the first time, to our knowledge, that HTLV-1 proviral loads in patients with other neurological abnormalities are also significantly higher than in asymptomatic HTLV-1 carriers.