A series of thirty-two cases is reviewed, all originally considered to be osteoclastoma. Fifteen are accepted as genuine osteoclastoma, the rest assigned to various categories of “giant-cell tumour variant.” Some problems in the radiation treatment of osteoclastoma are discussed, and detailed results of the cases given. The following “variants” are also discussed, with special reference to their radiation treatment:—simple cyst and fibrous dysplasia, giant-cell epulis, aneurysmal bone cyst, tumours in hyperparathyroidism, benign osteoblastoma (giant osteoid osteoma).