A case of acute adult T-cell leukemia-lymphoma (ATLL) was observed in northeast Italy, presenting with fever, lymphadenomegaly, splenomegaly, hypercalcemia and renal failure. Leukaemic cells were morphologically typical, expressed a T-cell CD4+ phenotype, did not display any helper functions, and grew in vitro under supply of exogenous interleukin-2. Antibodies to human T-cell lymphotropic virus (HTLV-I) were found in the serum, and the virus was isolated from leukaemic cells. The family members who could be tested were seronegative. The patient had never travelled outside Italy, had never received blood transfusions and did not belong to any known categories at risk of viral disease transmission. Present knowledge of the epidemiology of HTLV-I infection warns that other cases of HTLV-I induced disease are expected to occur outside already recognised endemic areas. This case suggests that untraceable, presumably short-term exposures can also account for HTLV-I transmission.