T-cell lymphoma composes 25% of lymphoid malignancies in Japan. Peripheral T-cell lymphoma (PTCL) unspecified and adult T-cell leukemia/lymphoma (ATLL) are major subtypes of T-cell lymphoma. The Japan Clinical Oncology Group (JCOG) has conducted 7 clinical trials for aggressive non-Hodgkin's lymphoma (NHL) including T-cell lymphoma. JCOG trials revealed that patients with ATLL had an extremely poor prognosis as compared with other peripheral T-cell lymphomas. A second generation combination chemotherapy including pentostatin (JCOG9109) could not improve the prognosis of patients with aggressive ATLL with the median survival time (MST) of 7.4 months. Subsequently, JCOG developed a new alternating multi-agent chemotherapy including MCNU and carboplatin with prophyractic use of G-CSF, resulting 35% of CR rate and 31% of 2-year OS. Considering the poor prognosis of aggressive ATLL patients, allogeneic stem cell transplantation seems to be another promising approach for a cure of the disease. New active agents such as chimeric monoclonal anti-CCR antibody are under developing for PTCL and ATLL.