Anticardiolipin and anti-beta2GP1 antibodies were measured in 50 patients with HTLV-1-associated Myelopathy-Tropical Spastic Paraparesis (HAM-TSP) and the results were compared with those obtained for 34 HTLV-1-positive and 35 HTLV-1-negative controls, as well as 128 SLE patients. aCL but not anti-beta2GP1 was associated with HTLV-I infection. aCL was more prevalent than anti-beta2GP1 (32% vs. 8%) and was not associated with anti-beta2GP1 in HAM-TSP. IgA was the dominant isotype of aCL and anti-beta2GP1. The data suggest that tin HAM-TSP, IgA aCL are frequent and are associated with HTLV-1 infection.