Positron emission tomography (PET) is an established imaging method in oncology. PET/computed tomography (PET/CT) and PET/magnetic resonance imaging (PET/MRI) are hybrid techniques which combine morphological information obtained by CT and MRI with functional data provided by PET. Several PET radiotracers evaluating different metabolic pathways or receptor status can be used to assess endocrine tumors such as thyroid tumors or neuroendocrine neoplasms (NENs). This review is focused to describe the role of PET imaging using different radiotracers in patients with thyroid tumors and NENs. The role of PET imaging with different radiotracers in several endocrine tumors including thyroid tumors, gastroenteropancreatic neoplasms, lung neuroendocrine neoplasms, pheochromocytomas and paragangliomas, and multiple endocrine neoplasia syndromes has been described. Fluorine-18 fluorodeoxyglucose (18F-FDG) PET evaluating the glucose metabolism provides useful diagnostic and prognostic information in patients with thyroid tumors. Iodine-124 (124I) assessing the iodine metabolism may be used for dosimetry and diagnostic purposes in thyroid tumors. In patients with NENs specific radiotracers can be used for diagnostic purposes such as somatostatin analogues labeled with gallium-68 (68Ga-DOTA-peptides) evaluating somatostatin receptor expression and fluorine-18 fluorodihydroxyphenylalanine (18F-FDOPA) assessing the uptake, decarboxylation and storage of amine precursors. One advantage of 68Ga-DOTA-peptides PET is to select patients with well-differentiated and inoperable NENs for peptide receptor radionuclide therapy. 18F-FDG PET may provide useful prognostic information in patients with high-grade NENs. PET imaging with different radiotracers is a useful functional imaging technique in the work-up of several endocrine tumors.