Sideroblastic anemias are a heterogenous group of disorders characterized by the presence of sideroblasts in the bone marrow aspirate. Current classification schemes distinguish between diseases of the heme synthesis pathway and diseases of other mitochondrial pathways which can either be of primary origin (defects in mitochondrial DNA) or of secondary origin (defects in nuclear DNA). Although several distinct hereditary forms exist, sideroblastic anemias are most frequently acquired diseases and belong to the group of myelodysplastic syndromes with the propensity to develop into overt leukemia. Treatment is mainly supportive (vitamins, blood transfusions, cytokines) and only rarely are bone marrow transplantations performed. The molecular defects of a few hereditary forms have already been elucidated, but the genes involved in the acquired forms are still largely unknown.