Increased understanding of the biologic and clinical parameters that define subgroups of myelodysplastic syndromes has led to continuing refinement of classification strategies for diagnostic and prognostic use. The French-American-British classification, based primarily on morphology, was modified by the World Health Organization system to include the negative impact of multilineage dysplasias and higher blast counts. In addition, this system identifies a distinct clinical subgroup characterized by an isolated chromosome 5 deletion. The International Prognostic Scoring System was created to calculate prognosis, risk of transformation to acute myeloid leukemia, and median survival times. However, therapeutic decisions cannot be solely guided by these systems, and the clinician must decide whether the intent is curative or palliative. Clinical symptoms and degree of transfusion dependency will dictate the degree of therapeutic intervention.