T lymphomas are classified into two types from surface phenotype, thymic T (T1) and Peripheral T (T2) lymphoma, and T2 lymphomas, are furthermore subdivided to inducer/helper (Ti/h or T4) and cytotoxic/suppressor (Tc/s or T8) type. But even in ATLL (adult T cell leukemia/lymphoma) believed to be a model of Ti/h type, the heterogeneities of surface phenotype are reported frequently. All of the pleomorphic and lymphoblastic and a part of small cell, medium-sized cell, mixed and large cell types have a T-cell phenotype. In addition to these histologies, AILD/IBL/IBL-like T lymphoma, T-zone lymphoma and So-called Lennert's lymphoma also hold T-cell nature. The heterogenecity and the existence of the borderline area between neoplasm and reactive lymphadenitis or hyperplasia often confused the clinicians and hematopathologists. From our experience, forty nine percent 5 year survival of T lymphoma other than lymphoblastic and pleomorphic type suggests the propriety of classifying T lymphoma into high grade and intermediate grade malignancies. Treatment of T lymphomas are basically distinguishable to two categories, for T1 and T2 lymphomas. The treatment of T1 lymphoma should be an aggressive one including CNS prophylaxis. At present, the recommendable treatment of T2 lymphoma is to apply the best regimens obtained from B cell lymphoma study. As aggressive treatment for ATL does not always yield favorable results, the concept of therapy will become clear near future. An intensive supportive therapy including T-S prophylaxis should be combined actively in the treatment program.