The indications for 18F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) in the investigation of oncological1 and inflammatory2 diseases are increasing. As the number of FDG-PET scans performed rises, more unexpected FDG uptakes are reported, including those within the thyroid gland.3 In subjects without known thyroid pathologies, the prevalence of focal uptake varies from 0.1% to 4.8% among studies.4 Diffuse uptake, in 0.1–4.5% of PET-CT, has been related to benign processes such as chronic thyroiditis, Graves’ disease, and multinodular goitre.5 These thyroid incidentalomas are added to those already described in other imaging modalities, such as cervical CT, magnetic resonance imaging, and ultrasonography (US), in which they are reported in 16%6 and 19–46%7 of cases, respectively. In two reviews, the average malignancy rates of focal incidentalomas revealed with PET or PET-CT were similar (34.8% and 34.6%).4, 8 but with a broad range of prevalence among different publications. This risk of malignancy is higher than in incidental thyroid nodules identified on other imaging modalities, such as US (from 4.4% to 12%).9, 10 Even so, almost two-thirds of PET focal uptakes within the thyroid gland are related to benign diseases. Consequently, to differentiate between malignant and benign thyroid lesions, many researchers have evaluated the usefulness of semi-quantitative parameters used in PET, such as the maximum standard unit value (SUVmax), with highly discrepant conclusions.8 The wide disparity in this outcome and the heterogeneity reported on the prevalence of incidental thyroid uptakes led to a study in our environment. The study aimed to evaluate the prevalence of incidental thyroid uptakes (focal and diffuse) observed in PET-CT performed on patients without previously detected thyroid carcinoma and to analyse the risk of malignancy of incidentalomas and the usefulness of SUVmax for differentiating between benign and malignant lesions.