The study presents 6 cases of leukemia/lymphoma (with mature T-cells) corresponding to the diagnostic criteria of adult T-cell leukemia (ATL): adult age onset of leukemia/lymphoma, organomegaly but normal mediastinum, leukemic cells with typical morphology and phenotype hypercalcemia. The evolution of disease was severe of subacute with resistance or partial response to therapy. The virologic assays were positive according to the ELISA test in four cases of which two presented, according to the Western blot assay, HTLV-I infection. The epidemic aspect of this infection is discussed as well as the possibility of contamination and the geographic spread of the places of origin of the patients. Emphasis is laid on the young age (22-26 years) of three of the patients infected, as a peculiar feature of the disease in Romania.