Several studies have reported on the expression of somatostatin receptors in patients with differentiated thyroid cancer (DTC). The aim of this study was to evaluate the imaging abilities of a recently developed technetium-99m labelled somatostatin analogue, (99m)Tc-EDDA/HYNIC-TOC ((99m)Tc-TOC), in terms of precise localisation of disease. The study population comprised 54 patients (24 men, 30 women; age range 22-90 years) with histologically confirmed DTC who presented with recurrent or persistent disease as indicated by elevated Tg levels after initial treatment. All patients were negative on the iodine-131 post-therapy whole-body scans. Fluorine-18 fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) was performed in a subgroup of 36 patients. The study population consisted of two groups: Group A ( n=22) comprised patients with disease recurrence as shown by elevated Tg levels but without detectable pathology. In group B ( n=32), pre-existing lesions were known. Among the 54 cases, SSTR scintigraphy was true positive in 33 (61.1%), true negative in 4 (7.4%) and false negative in 17 (31.5%) cases, which resulted in a sensitivity of 66%. A total of 138 tumour foci were localised in 33 patients. The fraction of true positive (99m)Tc-TOC findings was positively correlated ( P<0.01) with elevated Tg levels (higher than 30 ng/ml). Despite two false positive findings, analysis on a lesion basis demonstrated better diagnostic efficacy with (18)F-FDG PET ( P<0.001); however, it also revealed substantial agreement between the imaging techniques [Cohen's kappa of 0.62 (0.47-0.78)]. In conclusion, scintigraphy with (99m)Tc-TOC might be a promising tool for treatment planning; it is easy to perform and showed sufficient accuracy for localisation diagnostics in thyroid cancer patients with recurrent or metastatic disease.