Aim: to evaluate the value of F-18 FDG PET/CT compared to conventional imaging in change the management of patients with differentiated thyroid cancer before radioactive iodine ablation. Material &Methods: This retrospective study was conducted on hundred twenty-four patients (92 females and 32 males), with pathologically proven DTC. Baseline whole body F-18 FDG PET/CT was done before RAI-131 therapy, then correlated with neck U/S and CT chest findings. Results: The study group included 92 female and 32 male patients. The F-18 FDG PET/CT was positive in 65 sites in 38 patients (thyroid bed in 22, 15 in cervical LN) and distant sites in 28 patients. Neck U/S and F-18 FDG PET/CT loco-regional assessment showed fair agreement with a statistical significance (P value of <0.001) in detecting regional nodal lesions but no significance difference in operative bed lesions. The degree of agreement of F-18 FDG PET/CT with CT chest results was also conducted using the Kappa test and it showed fair to moderate degree of agreement, F-18 FDG PET/CT results changed the management of 29 patients accounting for 23.4% of the patients. Conclusion: The initial F-18FDG PET/CT before RAI-131 ablation may change the management in some patients as compared to other imaging modalities in differentiated thyroid cancer and in planning for proper dose of radioiodine therapy. Key Words.: F-18 FDG PET/CT &DTC.