Forty-seven histologically confirmed cases of Ewing's tumour are reported, with typical age, sex and skeletal distributions. The disease-free survival curves are like those for osteosarcoma of corresponding types of bone, but with higher mortality. The two-year disease-free survival rates were 24 per cent for tumours of long bones and 5 per cent for those of other bones. Osseous metastases were most frequent, although the lung was the commonest single site involved. There were secondary deposits in lymph nodes in nine patients, possibly also in four more with mediastinal enlargement. Although initially radiosensitive, one-third of tumours recurred locally, almost always with the appearance of metastases. Neither whole bone irradiation nor high dosage alone ensures complete control of the primary tumour, and it is suggested that recently reported improved results of treatment should be attributed to adjuvant multi-drug chemotherapy. Inadequate control of the primary tumour diminishes the chance of survival and for some sites radical operation merits reconsideration.