This report concerns a 6-year-old child with severe dyseythropoietic anaemia and splenomegaly, apparently present since the first months of life. Striking anisopolikilocytosis was observed in the blood smear. The bone marrow showed marked erythroblastic hyperplasia with dyserythropoiesis. Ineffective erythropoiesis was demonstrated by ferrokinetic studies. Ultrastructurally erythroblasts appeared grossly abnormal. The clinical course was progressively worsening, necessitating repeated transfusions. The patient's father, also affected by a chronic anaemia of moderate degree since childhood, had a peripheral picture of anisopoikilocytosis, a shortened life span of the erythrocyte and in his bone marrow an erythroblastic hyperplasia with many atypical erythroblasts. His condition deteriorated because of persistent jaundice, biliary cholelithiasis, fibrosis and haemosiderosis of the liver. The clinical course, the pattern of the genetical transmission, the peculiar features of the erythroblasts disclosed by light and by electron microscope studies suggest that these cases represent a new type of congenital dyserythropoietic anaemia.