Human T-lymphotropic virus 1 (HTLV-1) infection has been associated with ATL and inflammatory diseases but remains a neglected health problem. HTLV-1 associated diseases were originally described as sporadic entities, but family aggregations have been reported. Viral, genetic, immunological and behavioral factors were used to explain family clusters, but until now a clear explanation remains uncertain. In the present study we report, for the first time, a family cluster of diseased persons presenting the infection across three generations associated with FAS -670A/G polymorphism.