A relationship between tumor volume and prognosis has been demonstrated in extraosseaous solid tumors, soft tissue tumors and Ewing's sarcoma. Fifty-five osteosarcoma patients, treated according to IOR-OS/NEO 3 protocol, have been studied in an attempt to verify if tumor volume is also a significant prognostic factor for the osteosarcoma of the extremities. Tumor volume was measured by CT-Scan. A trend towards a better prognosis for smaller tumors was observed, but no statistically significant differences were demonstrated according to the tumor size in the population studied. The authors conclude that for patients with osteosarcoma of the extremities, tumor volume can not be considered an adequate prognostic factor on the basis of which to tailor the chemotherapy treatment, as been recently proposed by other authors.