We conducted an epidemiological study of osteosarcoma in Sweden from 1971 to 1984 to investigate whether the typical features of the disease had changed. Of 294 osteosarcoma patients reviewed, 249 had primary skeletal tumours, and for these the mean annual incidence was 2.1 per million, without any clear trend over time. The mean male/female ratio for the period was 1.6 again with no consistent pattern over time; nor was there any significant change in the distribution of tumours according to location. The only feature which showed a significant change over the 14-year period was the mean age of the patients, being at its lowest (19 years) in 1972 and at its highest (40 years) in 1981. Excluding the 22 patients with craniofacial tumours, the remaining 227 also showed a significant increase in mean age. Analysis of the annual age distribution disclosed an increasing fraction of patients older than those in the classical age peak between 10 and 29 years. A large number of trials have shown improved survival in osteosarcoma over the last 15 years, which has been attributed mainly to adjuvant chemotherapy. The change we have observed in age distribution should also be taken into account in the evaluation of the results of treatment; it may be that older patients have a better prognosis.