Disease Overview: The myelodysplastic (MDS) are a very heterogeneous group of myeloid disorders characterized by peripheral blood cytopenias and increased risk of transformation to acute myelogenous leukemia (AML). MDS occurs more frequently in older male and in individuals with prior exposure to cytotoxic therapy. Diagnosis: Diagnosis of MDS is based on morphological evidence of dysplasia upon visual examination of a bone marrow aspirate and biopsy. Information obtained from additional studies such as karyotype, flow cytometry or molecular genetics is complementary but not diagnostic. Risk-stratification: Prognosis of patients with MDS can be calculated using a number of scoring systems. In general, all these scoring systems include analysis of peripheral cytopenias, percentage of blasts in the bone marrow and cytogenetic characteristics. The most commonly used system is the International Prognostic Scoring System. IPSS is likely to be replaced by a new revised score (IPSS-R) and by the incorporation of new molecular markers recently described. Risk-adapted therapy: Therapy is selected based on risk, transfusion needs, percent of bone marrow blasts, and, more recently, cytogenetic profile. Goals of therapy are different in lower risk patients than in higher risk. In lower risk, the goal is to decrease transfusion needs and transformation to higher risk disease or AML. In higher risk, the goal is to prolong survival. Current available therapies include growth factor support, lenalidomide, hypomethylating agents, intensive chemotherapy, and allogeneic stem cell transplantation. The use of lenalidomide has significant clinical activity in patients with lower risk disease, anemia and a chromosome 5 alteration. 5-azacitidine and decitabine have activity in higher risk MDS. 5-azacitidine has been shown to improve survival in higher risk MDS. A number of new molecular lesions have been described in MDS that may serve as new therapeutic targets or aid in the selection of currently available agents. Additional supportive care measures may include the use of prophylactic antibiotics and iron chelation. Management of progressive or refractory disease: At the present time there are no approved interventions for patients with progressive or refractory disease particularly after hypomethylating based therapy. Options include cytarabine based therapy, transplantation and participation on a clinical trial. Am. J. Hematol. 87:692-701, 2012. © 2012 Wiley Periodicals, Inc.