Although there have been several reports of the skeletal changes in erythroblastosis foetalis, agreement is not complete. The largest series to date consists of 17 cases. It is the purpose of the present writers to review the literature and to present the skeletal findings in 100 consecutive infants with this condition studied roentgenologically at the Denver Children's Hospital. Erythroblastosis foetalis is usually an easily recognized clinical syndrome in the offspring of an Rh negative mother with an Rh positive father. It can also occur as a result of incompatibilities of different major blood groups or subgroups. The firstborn child is rarely affected unless the mother has been previously sensitized by a transfusion of incompatible blood. The incompatibility of the maternal and fetal blood results in excessive fetal hemolysis with resulting hemolytic jaundice. Hepatosplenomegaly, petechiae, ecchymoses, and mucosal bleeding are other possible features. Kernicterus is likely to occur if the serum bilirubin attains a high level. The laboratory findings of macrocytic anemia, reticulocytosis, leukocytosis, elevated bilirubin, and occasionally thrombocytopenia usually are enough to confirm the clinical diagnosis. Review of the Radiologic Literature Attention was first drawn to the long bones in erythroblastosis foetalis by Caffey (2, 3) in 1939. He described 2 cases, in 1 of which there was a dense line across the ends of the shafts of the long bones, while the other showed, in addition, a narrow band of radiolucency in the shaft adjacent to the dense metaphyseal line. In 1942, Follis et al. (4) described 5 cases of erythroblastosis foetalis, in 3 of which a radiolucent line of varying width was demonstrated immediately shaftward to the denser metaphyseal end of the bone. These authors concluded, however, that the most striking radiographic and histologic change was the overall increase in the density of the bones, due to “an increase in the number and thickness of the trabeculae.” In 1949, Ritvo et al. (6) also stressed the finding of increased bone density. They state that this finding, along with others, can in certain instances lead to the diagnosis of erythroblastosis foetalis in utero. Also in 1949, Janus and Dietz (5) collected 17 cases of the disease, of which 9 showed distal metaphyseal density, though only 3 exhibited an adjacent parallel radiolucent line. No increased density of the shafts of the bones was noted and the authors emphasized that the transverse lines were nonspecific and could be simulated by a variety of conditions such as prematurity, syphilis, and bismuth poisoning. Samuel and Cohen (7), in 1950, and Savignac (8), in 1958, stated their belief that increased density of the fetal bones is of no value in the prenatal diagnosis of fetal hydrops.