Objective: To evaluate value of FOG-PET/CT in detecting recurrent/metastatic lesions in post-surgical OTC patients with high serum thyroglobulin and negative 131I whole body scan. Subject and method: A cross sectional, descriptive was carried out 69 post-surgical DTC patients with high serum thyroglobulin and negative 131I whole body scan whom already underwent 131I therapy in Department of Nuclear Medicine, No.108 Central Military Hospital. FOG-PET /CT was performed when patients was on thyroxine therapy. Result: 92 lesions detected in 43 patients (62.3 percent) with positive PET/CT scan compared to only 39 lesions in 26 patients (37.7 percent) detected on positive CT scan. The sensitivity, accuracy and NPV of FOG-PET/CT were 87 percent, 88 percent and 76 percent higher than those of CT (54.3 percent, 67.2 percent and 48.8 percent, respectively). Specificity and PPV of FOG-PET/CT (90.5 percent and 95.2 percent, respectively) were similar to those of CT (95.2 percent and 96.2 percent, respectively). SUVmax threshold with best diagnostic value were 4.5 (sensitivity 92.3 percent, specificity 100 percent). FOG-PET/CT had altered treatment plan in 33/49 patients (47.8 percent). Conclusion: FOG-PET/CT was very useful in detecting recurrent/metastatic lesions in post-surgical differentiated thyroid carcinoma patients with high serum thyroglobulin and negative 131I whole body scan.