Differentiated thyroid cancers (DTC) are generally malignant endocrine tumors with good prognosis. 50-68% of patients with DTC's have local or regional recurrences depending on the patient's risk factors. The aim of the work: was to assess the rule of initial PET/CT in patients with DTC, evaluate the PET/CT as compared to post ablative WBS in DTC. The study included 124 patients with essentially pathologically proven differentiated cancer thyroid patients who had undergone or near total thyroidectomy and was eligible for RAI ablative dose. Pathological details, TG levels and post ablative I-131 WBS results were also reviewed and compared to PET/CT results. A short follow up period ranged from 4-6 months was used as a reference to validate the results of the current study. Results: we found the majority were females (74.2%), The mean age was 42 years old, papillary thyroid cancer was the dominant type in (83.1 %). (55.6%) was of low risk according to ATA Risk stratification and of stage I, Serum TG levels varied widely from 0.04-13564 with a median value of 8.28 ng/ml. 38 patients out of 124 (30.6%) showed positive FDG uptake in following sites thyroid operative bed, cervical and mediastinal LNs, pulmonary and bone metastases with the majority of pathological FDG uptake being at the loco-regional area in 38 patients. It was observed that PET/CT had positive results in older age groups especially those above 50 years old, patients with elevated serum TG levels with a median value of 40 ng/ml, Hurthle cell type and Intermediate /High risk groups. Therefore, patients with such criteria are more likely to benefit from initial PET/CT prior to their RAI dose. No significant correlation between the metabolic parameters and the avidity of RAI-131 positive findings was found. In 38 patients positive PET/CT results led to re-staging of 12 patients (9.6 %) and changed the management in 30 patients (24.2%). Conclusions: PET/CT changed the management in around 25 % of Differentiated thyroid cancers (DTC) that helped in validating the "Theranostics" concept which aimed at individualized patient management to achieve the best outcome.