Aim and objective: Concomitant thyroid nodules and cancer found incidentally on 18-fluorodeoxyglucose (FDG) positron-emission tomography (PET-CT) in patients imaged for investigation or staging of malignancy have been progressively encountered. Maximum SUV (SUV-max) may aid diagnosis of concomitant thyroid malignancy. Materials and methods: PET/CT scans were reviewed between 2009 and 2014 in which FDG-avid thyroid incidentalomas were included. Patients who were investigated with biopsy or surgery were further assessed to determine the utility of SUV-max, mean, and nodule size as a determinate of malignancy. Results: A total of 325 of 35,586 patients were identified with FDG-avid thyroid incidentalomas (TI)–99 were investigated. The incidence was 0.88%. Forty nine were malignant, with a median SUV-max of 14.5 (range 2.7–60.4). Malignant nodules had higher median SUV-max than benign nodules at a threshold of 5 (p < 0.0001). Receiver operator curve (ROC) analysis demonstrated an area under the curve of 0.66 (95%CI 0.55–0.77, p = 0.005). The sensitivity and specificity were 73.4 and 46.9, respectively. The positive and negative likelihood ratio was 3.12 (95%CI 1.80–5.50) and a negative likelihood ratio of 0.38. Conclusion: As FDG-avid TI can demonstrate variable uptake, SUV-max is not a useful tool to discriminate benign from malignant TI. SUV-max should remain a theoretical adjunctive tool for predicting thyroid cancer. Clinical significance: The threshold for investigating PET-avid thyroid nodules with ultrasound and FNAC (in the context of primary nonthyroidal malignancy) should be determined by the prognosis of the primary malignancy.