The serendipitous detection, also called incidentaloma, of focal hypermetabolic abnormalities at 18F-fluorodeoxyglucose PET-CT of the thyroid gland is relatively frequent, estimated to be around 1.5-2% of the cases investigated. The prevalence of cancer cases appears to be very low, well below 1%. Considering that PET-CT is mainly performed in patients with –sometimes advanced- cancer, it is essential to refrain from extensive workups, with often limited impact as for the patient’s prognosis. To summarize, the work-up of focal abnormalities is similar to that of the usual workup of thyroid nodules, including rigorous ultrasound evaluation and, if deemed appropriate, fine-needle aspiration biopsy, as recommended by current guidelines. In patients with diffuse uptake, a general endocrinology workup, based on clinical and laboratory data, is recommended.