A 67-year-old female was admitted with fatigue. Peripheral blood examination showed severe pancytopenia. Bone marrow biopsy revealed hypoplastic marrow. She was diagnosed as having aplastic anemia. Steroid pulse therapy was not effective. After treatment with erythropoietin (EPO) and granulocyte colony-stimulating factor (G-CSF), blasts which were positive for CD13, CD33, CD34 and HLA-DR and negative for myeloperoxidase appeared in the peripheral blood. At this time, bone marrow biopsy revealed myelofibrosis with increased blasts. Chromosome analysis showed 46XX, add (1) (p36), add (1) (q44), -2, -5, del (7) (q11), -12, +3mar. She died of pneumonia despite chemotherapy with etoposide. Administration of EPO and G-CSF may have led to the rapid development of leukemia and myelofibrosis.