The multiinstitutional osteosarcoma study (MIOS), a randomized trial of adjuvant therapy for osteosarcoma with a concurrent control group, registered 113 patients from June 1982 to August 1984. Preliminary analysis of the study indicated a significant event-free survival advantage favoring immediate adjuvant chemotherapy, (P less than .001). For patients treated with surgery alone or with surgery and adjuvant chemotherapy, the lungs were involved in more than 80% of the relapses. Patients relapsing after surgery alone tended to relapse earlier (P less than .01), had more pulmonary nodules (P less than .01), and had more frequent bilateral pulmonary involvement (P less than .01) than those treated with immediate postsurgical adjuvant chemotherapy. However, patients relapsing after treatment with surgery alone experienced a significantly longer interval to further disease progression (P less than .01) and improved survival after relapse (P = .01) when compared with patients who relapsed after treatment with immediate adjuvant chemotherapy. The only factor predictive of survival after relapse was if the patient could be made surgically disease-free after initial relapse (P = .03).