Abstract : The primary clinical application of 18F FDG PET/CT ( 18Fluorine labeled flurodeoxyglucose positron emission tomography/computed tomography) in differentiated thyroid carcinoma is in the identification of active disease in thyroglobulin (Tg) positive (gt;10 ng/ml), whole body iodine scan negative patients. The impact of FDG PET/CT in diagnosis, surveillance, cure, and progression-free survival of differentiated thyroid carcinoma patients remains to be seen. Five main indications of FDG PET/CT in thyroid cancer have been recommended by revised American thyroid association guidelines 2009. This review aims to provide a complete picture of PET imaging in thyroid malignancies and enumerates each indication with literature review. This review also highlights recent advances in targeted molecular imaging. Currently differentiated thyroid cancer is best imaged using conventional single photon emission computed tomography-based radioiodine tracers ( 123I/131I). Although the utility of FDG PET in well differentiated thyroid cancer patients who are iodine negative but with raised Tg is well established, evidence is emerging on the advantages of FDG PET/CT in other histological types of thyroid malignancy, such as Hurthle cell, medullary, and the anaplastic malignancies. Novel PET radiotracers, such as 124Iodine (124I), 18F-DOPA (3,4-dihydroxy-l- phenylalanine), and 68Ga-DOTA peptides are revolutionizing the way thyroid malignancies are imaged. Newer concepts on targeted molecular imaging and theranostics are ushering in new possibilities for imaging and treating thyroid cancer. © 2013 The Japanese Society of Nuclear Medicine.