Richard J et al. - A case is presented of detection of a secondary thyroid cancer arising from a pulmonary adenocarcinoma by fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET). The need to investigate thyroidal hypermetabolic foci detected incidentally on PET scans is well established so as not to miss a primary thyroid cancer. However, as this case illustrates, the possibility of metastatic thyroid cancer, even though less common, should be considered.