The congenital dyserythropoietic anemias (CDAs) comprise a group of rare hereditary disorders of erythropoiesis, characterized by ineffective erythropoiesis as the predominant mechanism of anemia and by distinct morphological abnormalities of the majority of erythroblasts in the bone marrow. The classification in three types as proposed in 1968 is still valid, but there is genetic heterogeneity within each type, and there are additional variants of unknown genetic basis. CDA II is the most frequent, and the nonfamilial type of CDA III the rarest group. The genes of CDA II and CDA III were mapped to chromosome 20 and 15, respectively, and the gene of CDA I on 15q was recently cloned. Therapeutic decision making requires definition of the type, an estimate of individual severity, and presence of or risk for complications. Therapeutic measures include interferon-alpha for CDA I, splenectomy for CDA II, and iron depletion for all individuals at risk for secondary hemochromatosis.