The clinical courses of 193 patients with high-grade, non-metastatic osteosarcoma were reviewed to ascertain the evolution of the natural history of the disease. All patients had the primary lesion in the extremities and were treated at the Rizzoli Orthopaedic Institute between 1976 and 1982 with surgery alone (30 cases) or surgery plus adjuvant chemotherapy (163 cases). All patients were regularly followed at our Institute. One hundred and fourteen patients, of which 27 were treated with surgery alone and 87 treated with adjuvant chemotherapy, developed overt metastatic disease. No differences were found concerning the sites of the first relapse which, for approximately 90% of cases, were lungs in both groups. However, in the group of patients treated with adjuvant chemotherapy the development of overt metastatic disease, as compared to non-adjuvant patients, was delayed with time (13 vs 8 months) and the number of metastatic nodules in the lung at first relapse was reduced. This alteration in metastatic pattern due to adjuvant chemotherapy is important because it allows surgical resection of pulmonary metastases in a larger number of patients (51% vs 29%).