Two cases of acute myeloblastic leukemia (AML) evolving from aplastic anemia are presented. The first case was diagnosed 18 years ago, and treatment with bolus methylprednisolone, prednisolone, and androgens resulted in partial hematological response. Severe pancytopenia recurred, and AML M0 by French-American-British classification developed. The second case was diagnosed 7 years ago. The patient had HLA DRB1*1501, and treatment with granulocyte colony-stimulating factor (G-CSF), cyclosporine, and methenolone resulted in complete hematological response. Thrombocytopenia recurred and did not respond to cyclosporine and methenolone or to later treatment with antithymocyte globulin, and AML M1 developed. Cytogenetic studies demonstrated 7q- in the first patient and +8 in the second patient. No mutations of N-ras or p53 were observed in either patient. These patients were treated with cytosine arabinoside, aclacinomycin, and G-CSF (CAG) chemotherapy, and the number of leukemic cells decreased substantially. However, pancytopenia after CAG chemotherapy persisted, and the first patient died of pneumonia and the second patient of cerebral hemorrhage.