[en] In Ewing sarcoma, the addition of preoperative and postoperative chemotherapy has dramatically raised the 5-year survival rate. Radiologic evaluation of chemotherapy response becomes important so that the treatment plan can be altered in cases of poor response. The authors evaluated sequential examinations, including plain radiographs, Tc-99m skeletal scintigrams, and CT scans in 48 patients with Ewing sarcoma of bone. In 31 patients, biopsy material was obtained for histologic grading of treatment response. Good tumor response (grades 3 and 4) led over the ensuing 1-3 months to disappearance of the soft-tissue tumor component, solid transformation of the previously lamellated or spiculated periosteal reaction, and filling in of the lytic regions. Insufficient tumor response (grades 1 and 2) demonstrated persistence of soft-tissue tumor component and lamellated or spiculated periosteal reaction as well as absence, filling in, or even enlargement of lytic regions