A 25-year-old man was referred because of skin rash, lymphadenopathy and anemia. Laboratory examinations revealed severe anemia (Hb, 4.8 g/dl) and elevated levels of GOT, GPT, LDH and soluble interleukin-2 receptor. Work-up studies disclosed the involvement of lymphoma cells in lymph nodes, skin, bilateral kidneys and bone marrow. Lymph node biopsy revealed diffuse proliferation of medium- to large-sized lymphoblastic cells. Bone marrow aspiration showed massive infiltration of large blastic cells with no cytoplasmic granules. The lymphoma cells in bone marrow and lymph node showed surface CD3-, cytoplasmic CD3epsilon+, CD4+, CD8-, CD56+, CD57-, CD16- and CD43 (MT-1)+ phenotype. Analyses of T cell receptor beta and gamma genes showed germ line configurations. EBER-1 was not detectable in the lymphoma cells. He was diagnosed as having blastoid natural killer (NK) cell lymphoma. In spite of several courses of combination chemotherapy, the lymphoma was progressive. He was then treated with high-dose chemotherapy and peripheral blood stem cell rescue, achieving remission which has now lasted for more than 12 months. We consider that blastoid NK cell lymphoma is an extremely aggressive subtype of CD56-positive lymphomas, and high-dose chemotherapy with peripheral blood stem cell rescue should be included for the choice of the treatment.