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The objective of this retrospective study was to compare positron emission tomography/computed tomography using fluorine-18-fluorodeoxyglucose (18F-FDG-PET/CT) and conventional imaging modalities (CIM) in initial staging and early assessment of response to chemotherapy in children and young adults treated for rhabdomyosarcoma (RMS).At initial staging, 23 patients (9 months to 21 years) with histologically proven RMS underwent 18F-FDG-PET/CT in addition to CIM (MRI of the primary site, whole-body CT, and bone scintigraphy). After three courses of chemotherapy, 13 patients underwent 18F-FDG-PET/CT in addition to CIM. RECIST criteria and visual analysis of 18F-FDG uptake were used for assessment of response. The standard of reference was determined by an interdisciplinary tumor board on the basis of imaging material, histopathology, and follow-up data (median=5 years).18F-FDG-PET/CT sensitivity was superior to that of CIM for determination of lymph node involvement (100 vs. 75%) and detection of metastases (100 vs. 66%). 18F-FDG-PET/CT results changed therapeutic management in 13% of cases. After three courses of chemotherapy 18F-FDG-PET/CT was able to detect 92% of objective responses compared with 84% by CIM. The rate of complete response was 69% with 18F-FDG-PET/CT compared with 8% with CIM.This study confirms that 18F-FDG-PET/CT reveals important additional information at initial staging of pediatric RMS, which suggests a superior prognostic value of 18F-FDG-PET/CT in early response to chemotherapy assessment.