The aim of this study was to identify predictive factors of late relapse in nonmetastatic osteosarcoma patients treated at the Rizzoli Institute from 1983 to 1997. Clinical features of patients who had late (>4 y of follow-up) or earlier recurrence were compared. Late relapse was reported in 24 (3.7%) of the 648 patients who entered the studies. A surgical complete remission was achieved in 19 (79%) patients. The 5-year probability of postrelapse survival was 65% for the complete remission patients (48% in the entire group), which was significantly better than that of the patients (5-year postrelapse survival 20%) with an early relapse. Sex, site, and size of the tumor, histologic subtype, alkaline phosphatase and lactate dehydrogenase serum levels, type of surgery, and histologic response did not significantly differ between patients with late or early relapse. No clinical predictive factors of late relapse were identified and a prolonged follow-up is recommended for all patients.