Myelodysplastic syndromes (MDS) are a group of clonal neoplasms with maturation defects characterized by dysplasia, cytopenia, and immature bone marrow precursors. Myelodysplastic syndromes can be idiopathic, or secondary to various injurious exposures such as cytotoxic chemotherapy, ionizing radiation, or environmental toxins. The median patient age is 70 years old. Presentation includes symptoms of anemia (fatigue), neutropenia (infection), or thrombocytopenia (bleeding). The diagnosis is based on bone marrow evaluation, which reveals cytopenia, dysplasia in at least 1 lineage, and blast cells in < 20% of marrow cellularity. Cytogenetic and molecular studies are required for classification, prognosis, and therapy-related decisions. An increased cumulative risk of transformation to AML is present and varies depending on MDS subtype. Management includes supportive care, use of hematopoietic growth factors, immunosuppressive therapy, and allogeneic hematopoietic cell transplantation.