Acquired amegakaryocytic thrombocytopenic purpura is a rare disorder characterized by severe thrombocytopenia due to the absence of bone marrow megakaryocytes. The pathogenic mechanisms of this disorder have not well defined; consequently, several empirical therapies are used. We reported the case of a 38-year-old mean who was hospitalized for serious bleeding syndrome. The platelet count was 10 yen10(9)/L. The bone marrow aspirate and biopsy showed the absence of megakaryocytes but otherwise normal granulocyte and erythroid precursors. No definable etiology has been found. After the unsuccessful use of prednisone, intravenous immunoglobulin therapy was started and resulted in favorable reponse.