Two types of pathologic changes may occur in the long bones of patients with sickle cell anemia. A hyperplastic bone marrow represents the response to continued destruction of erythrocytes and this produces a wide medullary cavity and a thin cortex. The thromboses of vessels in the marrow and bone result in abnormal areas of calcification and new bone formation producing a thick cortex and a small medullary cavity. The findings on roentgenographic examination will depend upon which of the two processes is dominant. A 21 month old Negro infant whose symptoms of sickle cell anemia began at 4 months of age showed typical roentgenographic findings resulting from a hyperplastic marrow. The cortex in the femur had become so thin that a pathologic fracture resulted. This is the first reported instance of the occurrence of a pathologic fracture in sickle cell anemia.