The myelodysplastic syndromes are clonal hematologic disorders characterized clinically and morphologically by ineffective hematopoiesis. The natural history of these syndromes ranges from a chronic course that may span years to a rapid course of leukemic progression. Unfortunately, the nomenclature and classification systems used to describe these conditions are cumbersome and contentious. Nonetheless, myelodysplastic syndromes are viewed by most hematologists as encompassing stages of neoplastic hematopoiesis associated with cytopenias and as excluding nonneoplastic conditions. In general, myelodysplastic conditions are preleukemic disorders in which the neoplastic clone is established, but not all cases of myelodysplasia terminate in acute myeloid leukemia (AML). Here, . . .