We present a case of angioimmunoblastic T cell lymphoma (AITL) with autoimmune thrombocytopenia. A 85-year-old man was admitted to our hospital with thrombocytopenia, generalized lymphadenopathy, pleural effusion, and splenomegaly in June 2000. Blood chemistry revealed hemoglobin and platelet counts of 8.8 g/dL and 26 x 10(9)/L, respectively. The level of platelet-associate-IgG was 2568.9 ng/10(7) cells. The direct Coombs test was positive. The level of serum IL-6 was 10.2 pg/ml. Megakaryocytes in the bone marrow increased. Lymph node biopsy showed diffuse proliferation of atypical lymphoid cells with a clear cytoplasm accompanied by plasma cells and small vessels. He was diagnosed as having AITL with autoimmune thrombocytopenia and hemolytic anemia. He received repeated platelet transfusion, and a limited effect of prednisolone therapy on his platelet count was observed. Combination chemotherapy lessened the extent of the lymphadenopathy and slightly elongated the interval of platelet transfusion. We next performed splenic irradiation and a slight increase in the platelet count was observed. He died of pneumonia in August 2000. Autoimmune thrombocytopenia associated with AITL is rare and the therapy containing prednisolone and chemotherapy is reported to be partly effective. Our case showed a minor response of autoimmune thrombocytopenia to splenic irradiation. Therapeutic intervention for hypersplenism should be considered if thrombocytopenia is not improved by chemotherapy alone.