Although thyroid cancer is a comparatively rare malignancy, it represents the 
vast majority of endocrine cancers and its incidence is increasing. Most 
differentiated thyroid cancers have an excellent prognosis if diagnosed early 
and treated appropriately. Aggressive histologic subtypes and variants carry a 
worse prognosis. During the last 2 decades positron emission tomography (PET) 
and PET/computed tomography (CT), mostly with fluorodeoxyglucose (FDG), has been 
used increasingly in patients with thyroid cancers. Currently, the most valuable 
role FDG-PET/CT exists in the work-up of patients with differentiated thyroid 
cancer status post thyroidectomy who present with increasing thyroglobulin 
levels and a negative (131)I whole-body scan. FDG-PET/CT is also useful in the 
initial (post thyroidectomy) staging of high-risk patients with less 
differentiated (and thus less iodine-avid and clinically more aggressive) 
subtypes, such as tall cell variant and Hürthle cell carcinoma, but in 
particular poorly differentiated and anaplastic carcinoma. FDG-PET/CT may help 
in defining the extent of disease in some patients with medullary thyroid 
carcinoma and rising postoperative calcitonin levels. However, FDOPA has emerged 
as an alternate and more promising radiotracer in this setting. In aggressive 
cancers that are less amenable to treatment with (131)iodine, FDG-PET/CT may 
help in radiotherapy planning, and in assessing the response to radiotherapy, 
embolization, or experimental systemic treatments. (124)Iodine PET/CT may serve 
a role in obtaining lesional dosimetry for better and more rationale planning of 
treatment with (131)iodine. Thyroid cancer is not a monolithic disease, and 
different stages and histologic entities require different approaches in imaging 
and individualized therapy.