Adult T-cell leukaemia is the first blood disease caused by a retrovirus: HTLV-1. The authors report the first French series of 15 patients, of whom 9 came from the classical endemic areas--the Antilles and outer Caribbean Islands--and 6 from Africa where the serological prevalence of HTLV-1 is high but few cases of adult T-cell leukaemia have been reported. Emphasis is laid on the importance of immunodeficiency (refractory strongyloidiasis, Pneumocystis carinii pneumonia, polyclonal B lymphoproliferative syndrome) and of other pathologies associated with the retrovirus (polyarthritis, lymphocytic interstitial pneumonia). The authors also describe the presence of adenopathy in healthy carriers: either adenitis suggestive of retroviral infection, or Castelman's disease adenopathy. These clinical presentations are similar to those described in lymphadenopathy syndromes due to the human immunodeficiency viruses. Aggressive lymphomas require chemotherapy, but sooner or later resistance develops, and the prognosis is very poor. The indications for allogeneic bone marrow transplantation are still to be determined. The diagnosis of adult T-cell leukaemia must be considered in all patients with blood disease coming from the endemic areas.