A male with myelodysplastic syndrome (MDS) following aplastic anemia is reported. The patient had been diagnosed as aplastic anemia at 8 years of age, and treated with blood transfusions, anabolic and glucocorticoid steroid hormones. Over a period of subsequent twelve years, he had remission and deterioration. At the age of 21, the patient developed a sudden progression of severe anemia, when his bone marrow showed hyperplasia with prominent dyshematopoiesis and excess of blasts, compatible with MDS by the definition of FAB classification. He received low dose Ara-C therapy, which was ineffective. Nine months later he developed acute monocytic leukemia (M5b) and died. Chromosomal analysis revealed 46, XY at the onset of aplastic anemia, 46, XY, del (6) (q21 q27) at the MDS and 46, XY, -7, +21, 6q-/47, XY, +Y, -7, +21, 6q- at the acute leukemic stage.