More than 25 years have passed since adult T-cell leukaemia-lymphoma (ATLL) was identified as a distinct clinical entity clustered in the southwestern part of Japan. During these years, its causative agent, Human T-cell leukaemia virus type I (HTLV-I), was found, and remarkable clinical variance of this disease was recognized afterward. Because of the regional occurrence of this disease in the world, young medical scientists whose community is not endemic for this disease may have little understanding of it and may think that it a T-lymphoblastic leukaemia-lymphoma of adult-onset. In Nagasaki prefecture in Japan, where HTLV-I carriers account for 3-5% of the population, the incidence of ATLL is almost the same as the incidence of B-cell lymphomas, and hence ATLL is a matter of major concern. In contrast to the vast accumulation of knowledge about the oncogenic role of HTLV-I and molecular biology of ATLL cells, improvement in the prognosis of patients has not been satisfactorily achieved except for some recent progression. Here, we review the current status of therapy for ATLL in Japan and discuss how best to manage this difficult disease at this point and what next step should be taken.