Congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of rare hereditary disorders of erythropoiesis characterized by morphologic abnormal erythroblasts in the bone marrow. Three types of the disease are known as type I, II and III, and the variant type of CDA and several minor subgroups of CDA have been also reported since the first classification. Recently, responsible genes for type I (CDAN1) and type II (SEC23B) have been identified and the molecular pathogenesis of the disease is currently being explored. Although CDAs rarely transform to myelodysplastic syndrome or leukemia, the disease is important to understand the mechanism of hemopoiesis in humans.