Abstract Aim To evaluate the utility of 18F FDG-PET for patients diagnosed of differentiated thyroid carcinoma who present risk of disease and invaluable levels of thyroglobulin (Tg) by the presence of antibodies antithyroglobulin (AbTg). Material and methods Retrospective study of 7 women of 40 years old and histological diagnosis of differentiated thyroid cancer (7 papillary tumours) that were sent to our department for the accomplishment of 18F FDG-PET study because of suspicion of disease, due to 131 I negative and high levels of AbTg, between the year 2002 and 2007. 11 PET scans were obtained after the intravenous injection of 370–434 MBq of 18F FDG in normoglycemia conditions and previous administration of muscle relaxant, hydration and diuretic. The results of 18F FDG-PET scans were confirmed by pathologic examination or clinical outcome and radiographic examination for more than 24 months. Results The prevalence of recurrence in our population was 57.14%. All patients presented levels of Tg lower than 3 ng/dl and AbTg superior to 200 UI/ml. Three patients had precedent thyroiditis. Out of 11 scans performed 3 of them were negative and 8 cases were found positive. It ruled out the existence of disease in three patients and localized the presence of recurrence in 4 patients. Conclusion 18F-FDG-PET is a useful diagnostic tool for the detection of recurrence as well as to rule out the existence of disease with a high accuracy, in patients with differentiated thyroid carcinoma with 131 I whole body scan negative but with pathological elevation of antithyroglobulin antibodies.