Typical features of congenital dyserythropoietic anaemia (CDA) were found in a 13-year-old girl admitted for chronic recurrent multifocal osteomyelitis. The findings on light microscopy were in agreement with those described in CDA type II, whereas on electron microscopy, the ultrastructure findings were compatible with both types I and II. The acidified serum lysis test (Ham test) performed with eight normal sera was negative. The patient's red blood cells showed an increased agglutinability with anti-i antibodies. Morphological changes were also shown in the mature neutrophilic granulocyte suggesting that the primary disorder exists already in the multipotent stem cell.