The autopsy and electron microscopic findings in a pair of brothers with congenital dyserythropoietic anemia (CDA) are presented. In both patients autopsy revealed severe secondary hemochromatosis, including cirrhosis of the liver and fatal heart involvement. According to current ultrastructural criteria, a mixture of CDA type I (interchromatin bridges, wide euchromatin-cytoplasmic connections) and of type II (marginal cisternae, nuclear protrusions, multinuclearity, karyorrhexis) was found in erythroblasts of one patient. In the second patient electron microscopy of bone marrow stored in formalin for several years allowed the diagnosis of CDA with marginal cisternae in retrospect. These findings illustrate the usefulness of electron microscopy for the diagnosis of CDA in unsolved cases of chronic ineffective erythropoiesis, even from formalin fixed material. For subtyping CDA into type I and II, however, other than morphological parameters should be used for definition. In the clinical management splenectomy and a drastic phlebotomy programme have been found favourable.