Medullary thyroid carcinoma (MTC) is a neuroendocrine tumour characterized by the production and secretion of calcitonin. MTC tumours may express functional somatostatin receptors (hSSTR). A significant proportion of hSSTR receptor-positive MTC tumours, including metastatic disease, may be visualized in vivo through 111In-pentetreotide scintigraphy. Four patients with recurrent/metastatic disease, who had previously been assessed with 111In-anti-CEA monoclonal antibody fragment [F(ab')2] imaging, were evaluated. 111In-pentetreotide scintigraphy localized all known disease sites. Furthermore, mediastinal disease was detected in one patient with negative conventional, and 111In-anti-CEA F(ab')2 imaging studies. The detection of somatostatin within the tumour (2 patients), or negative octreotide challenges (2 patients), did not affect the outcome of 111In-pentetreotide scintigraphy. In conclusion, 111In-pentetreotide scintigraphy appears at least as effective as 111In-anti-CEA F(ab')2 imaging and should be considered in the diagnostic evaluation of MTC, particularly in the setting of recurrent/metastatic disease not detected by conventional means.