Thyroid carcinomas account for 1% of all malignant neoplasms and are the most common of all malignant thyroid neoplasms. Positron emission tomography/computed tomography (PET/CT) can be used in the diagnosis of thyroid cancer in cases of suspected disease recurrence and distant metastases. PET/CT provides an image of the function, size, morphology and anatomical location of the tumor lesion. The indication for use in differentiated thyroid cancers, such as papillary and follicular, is an elevated serum thyroglobulin level of more than 10 ng/mL in patients who have been treated with total thyroidectomy and radioactive ablation with negative 131I scintigram. Radiopharmaceuticals used in the diagnosis of differentiated thyroid cancers are fluorine-18-fluorodeoxyglucose (18F-FDG) in iodine-negative cancers and iodine-124 (124I) or fluorine-18-tetrafluoroborate (18F-TFB) in iodine-positive cancers, if available for clinical application. 18F-FDG-PET/CT has prognostic significance, as a higher uptake of fluorodeoxyglucose in the cells indicates a less differentiated and more aggressive thyroid carcinoma with a poorer prognosis. Radiopharmaceuticals used in the diagnosis of medullary carcinoma are fluorine-18-fluorodeoxyglucose (18F-FDG), fluorine-18 fluorodopa (18F-DOPA) and gallium-68 analogs of somatostatin. The indication for use in medullary carcinoma is elevated calcitonin and CEA levels in serum with negative radiologic findings in the case of suspected metastases in the body. The use of 18F-DOPA PET/CT is recommended when calcitonin is elevated and 18F-FDG PET/CT when CEA is elevated. In the case of anaplastic carcinoma, 18F-FDG PET/CT is used to assess the extent and resectability of the tumor, as well as the therapeutic response.