Human T-lymphotropic virus, type 1 (HTLV-1) infection was detected in two unrelated Kuwaiti patients with tropical spastic paraparesis (HAM/TSP) and in the asymptomatic mother of one of them. The family roots of these patients were traced to the Najaf region of Iraq. The DNA sequence of three PCR-amplified fragments (env, 512 bp; pol, 140 bp; LTR, 704 bp) was determined for each of Kuwaiti HTLV-1 isolates (KUW-1,2,3). All three Kuwaiti HTLV-1 were identical in env and pol fragments and virtually identical in LTR. Two rare substitutions were found in the env and pol fragments. They were shared only with two isolates from Reunion Island (substitution in env), and two isolates from India and the Caribbean (substitution in pol). The sequences of env and pol fragments of the Middle Eastern HTLV-1 isolates were not available. However, the comparison of Kuwaiti isolates with representative Middle Eastern HTLV-1 was possible for the LTR fragment. The phylogenetic analysis of LTR sequences of KUW and 34 other HTLV-1 isolates has shown that Kuwaiti HTLV-1 belongs to a cosmopolitan "a" subtype of HTLV-1 and tends to cluster together with HTLV-1 originating from the Mashhad region of Iran. These results suggest that common origin of Mashhadi and Kuwaiti (Najafi) HTLV-1 and the possibility of another pocket of HTLV-1 infection in the Middle East, located in the Najaf region of Iraq.