One hundred and seventy-eight cases of unicameral bone cysts (UBC) treated with curettage and bone grafting were compared to 141 cases treated with cortisone injections. The end results were comparable in the two groups. Local recurrence risk factors in the surgical group were active cyst and previous operations. In the other group they were multilocation of the cyst, active cyst, and size of cyst. A new radiographic classification of aneurysmal bone cyst (ABC) is proposed in a report of 198 cases of ABC. The treatment of choice in ABC is surgical and the type (curettage, curettage plus phenole or cryosurgery, resection or hemiresection) is selected on the basis of the radiographic aspect and the rate of growth of the cyst. Radiotherapy is only indicated in inoperable ABC cases.