The association between the oncogenic human retrovirus HTLV-1 and a form of tropical spastic paraparesis (TSP) of unknown etiology (frequent in French West-Indies) was demonstrated by our laboratory in 1985. A year later, the association of HTLV-1 with a chronic spastic myelopathy was documented in Southern Japan, and this clinical entity was named HTLV-1 associated myelopathy (HAM). It was then recognized that HTLV-1 associated TSP and HAM were the same disease, the hybrid term TSP/HAM was adopted and WHO diagnostic criteria were established.