A case of acute megakaryoblastic leukemia with complex chromosomal aberrations is reported. A 63-year-old man was admitted to our hospital because of pancytopenia. Bone marrow aspiration resulted in a dry tap and biopsy showed hypoplastic marrow with fibrosis. Blast cells in the peripheral blood were identified as megakaryoblasts because they were positive for electron microscopic platelet peroxidase (PPO). In addition, monoclonal antibody, TP80, to platelet glycoprotein II b-III a reacted with in about 26% of the blast cells. Chromosomal analysis of the peripheral blood revealed a mosaic pattern of a normal karyotype and abnormal ones, including 44, XY, -5, -7, -18, 10q-, +marker.