BACKGROUND: Response to neoadjuvant chemotherapy is a significant prognostic factor for osteosarcoma (OS) and the Ewing sarcoma family of tumors (ESFT). Conventional radiographic imaging does not discriminate between responding and nonresponding osseous tumors. [F-18]-fluorodeoxy-D-glucose (FDG) positron emission tomography ( PET) is a noninvasive imaging modality that accurately predicts histologic response in patients with various malignancies. We aimed to analyze the FDG PET imaging characteristics and to determine the correlation between FDG PET imaging and chemotherapy response in children with bone sarcomas. METHODS: Pediatric patients with OS (n=18) or ESFT (n=14) were evaluated by FDG PET. All patients received neoadjuvant chemotherapy. FDG PET standard uptake values before (SUV1) and after (SUV2) chemotherapy were analyzed and correlated with chemotherapy response assessed by histopathology in surgically excised tumors. Twenty-six patients had SUV1, SUV2, and surgical excision. RESULTS: While mean SUV1 were not different between OS and ESFT (10.7 i＞기울림꼴/i＞. 6.7, P=0.20), SUV2 were greater in children with OS than in those with ESFT (4.8 i＞기울림꼴/i＞1.5, P=0.04). All ESFT patients and 50% of OS patients showed a favorable histologic response to chemotherapy (≥90% necrosis). The ratio of SUV2 to SUV1 (SUV2:SUV1) were 0.61 for OS and 0.27 for ESFT. SUV2-SUV1/SUV1≥ 0.5 and SUV2＜ 2.4 correlated with favorable histologic response ( P0.001 and 0.003, respectively). CONCLUSION: SUV2 correlated with histologic response and could be used as a noninvasive surrogate to predict response in pediatric patients with bone sarcomas.