The authors analysed the patterns of recurrence of osteosarcoma of the extremities treated between 1959 and 1989 either with surgery alone (1959-71) or with combined surgery and adjuvant (1972-82) or neoadjuvant chemotherapy (1983-89). In a total of 452 patients with recurrent osteosarcoma, the initial site of metastasis was the lung in 88% of cases independently of the type of treatment received. The mean period of onset of pulmonary metastasis differed according to the type of treatment performed: 8 months for patients treated with surgery alone; 15.9 months for those treated with adjuvant chemotherapy and 20.3 months for patients treated with neoadjuvant chemotherapy. The incidence of metastases appearing within 12 months of FU was 87%, 56% and 21% respectively. In a most recent and effective neoadjuvant protocol (66% DFS), the incidence of recurrence owing to pulmonary metastasis during the first year of FU was 2% and as much as 75% of all recurrences were concentrated in the following 18 months. Surgery for pulmonary metastasis in patients undergoing chemotherapy was performed in 54 cases with secondary healing in 14 (26%). On the basis of these results the authors suggest a scheme of radiological follow-up for patients with osteosarcoma of the extremities treated with neoadjuvant chemotherapy with intensified controls (every 2 months) during the period with the highest risk of recurrence (13-20 months) and four-monthly controls during the first year and after 31 months of FU. In order to increase the efficacy of FU controls during the high-risk period, the a. propose using CT controls instead of chest X-rays at months 14, 20 and 26.