[en] Clinical results of intraoperative radiotherapy (IOR) for malignant bone tumors and soft-tissue sarcomas are reported. Of a total of 40 cases of malignant bone tumors and soft-tissue sarcomas treated by intraoperative radiotherapy, 20 were malignant bone tumors, mostly osteosarcomas. These lesions were surgically opened and irradiated with a single dose (50 Gy) by an electron beam. Radical surgical procedures, amputation or limb-saving procedures with endoprosthesis, were carried out two to 10 months after intraoperative radiotherapy in 11 of these patients ; the remaining nine received intraoperative radiotherapy alone. In only two of the cases of malignant bone tumor was there local recurrence, probably because of defective irradiation in one case and implantation during biopsy in the other. The results of histological examination to accurately assess the therapeutic effect of intraoperative radiotherapy in the 11 patients who had undergone en block resection, amputation, or autopsy after irradiation strongly suggested that intraoperative radiotherapy is extremely effective in controlling local malignant bone tumors. The remaining 20 cases were soft-tissue sarcomas in which wide resection of the lesion was performed and a single dose (20 to 45 Gy) of intraoperative radiotherapy was administered by an electron beam. Ten of these patients had recurrence. Recurrence was noted mainly in surgically difficult cases, however, cases in which complete resection or proper irradiation was not possible. Thus, while the overall rate of local control achieved in malignant bone tumors treated with intraoperative radiotherapy was satisfactory, about 90 %, it was only 50 % in soft-tissue sarcomas treated with intraoperative radiotherapy. This low rate indicates the need for further study to improve methods of irradiation and surgery. (author)