Although several clinicopathologic parameters may be related to metastasis-free survival in osteosarcoma, the importance of prognostic factors with time is largely unknown. Therefore, we asked whether the clinical characteristics of patients with osteosarcoma with metastasis after 2 years differed from those of patients with an earlier metastatic event. We retrospectively reviewed 420 patients with Stage IIB osteosarcoma treated with surgery and chemotherapy. The minimum followup was 3 months (mean, 71.4 months; range, 3-257 months). Among the 420 patients, 167 patients had a metastatic event. A large proportion (43%) of the 35 good responders showed metastasis after 2 years, whereas 24% of the 96 poor responders showed late metastasis. Histologic response and chondroblastic subtype showed time-related changes. Poor histologic response showed a gradual decline in prognostic value and lost its importance after 2 years. Most metastatic events occurred within 2 years after diagnosis; therefore, we recommend new predictive strategies and followup protocol for patients experiencing late relapse.