After total thyroidectomy followed by radioiodine ablation, 30 consecutive patients with differentiated thyroid cancer, elevated serum thyroglobulin levels and negative whole body radioiodine scan underwent (18)F-FDG-PET/CT. Results were verified by histology, ultrasound, or clinical follow-up. Diagnostic accuracy was determined for the whole study population and for subgroups with serum thyroglobulin below and above 10 ng/ml, respectively. Impact of PET/CT on clinical management was assessed.