1. The bone changes are described in fifty-one cases of sickle cell anaemia. nineteen cases of sickle cell haemoglobin C disease and two cases of sickle cell thalassaemia.

2. Avascular necrosis of the head of the femur has been found in all three types of sickle cell disease. These responded to treatment.

3. The changes found in six cases of Perthes' disease in the negro are compared with the changes in avascular necrosis of the head of the femur in sickle cell disease.

4. Hyperplastic bone changes are seen only in true sickle cell anaemia and not in the variants.

5. Secondary osteomyelitis appears to be fairly common in sickle cell anaemia. Organisms of the salmonella group have often been found in these cases.