In patients with gastro-enteropancreatic neuroendocrine tumours the localization of all the neoplastic lesions and an accurate staging of the diseases have important therapeutic implications. Somatostatin receptor scintigraphy with In-111 pentatreotide has proved to be useful in detecting gastro-enteropancreatic tumours; however, the role of abdominal single photon emission computed tomography has not yet been definitively established. In a series of 52 patients with gastro-enteropancreatic tumours (9 non-functioning islet cell carcinomas, 4 insulinomas, 3 somatostatinomas, 2 VIPomas, 1 glucagonoma and 33 carcinoids) we compared somatostatin receptor scintigraphy with the results of computed tomography and magnetic resonance imaging performed within one month. Four and 24-hour total body planar images and 4-hour abdominal single photon emission computed tomography were acquired after the i.v. injection of approximately 250 MBq of In-111 pentatreotide. Only abdominal localizations were considered: planar scans detected 16 extrahepatic lesions in 13 patients and 54 liver sites in 21 patients; single photon emission computed tomography visualized 31 extrahepatic lesions and 89 liver metastases in 27 and 28 patients, respectively; computed tomography and magnetic resonance imaging detected 11 extrahepatic lesions in 10 patients and 73 liver sites in 21 patients. In-111 pentatreotide single photon emission computed tomography was the only imaging method able to localize tumoural lesions in 13 patients; all these localizations were then histologically verified. The scintigraphic positivity did not depend on the site or on the presence of hormonal hypersecretions. In conclusion, our results indicate that single photon emission computed tomography is more sensitive than planar images and computed tomography/magnetic resonance imaging in detecting abdominal gastro-enteropancreatic tumours and their metastases; it is able to increase both the number of visualized lesions and that of patients with positive findings. Single photon emission computed tomography is particularly useful in patients in whom tumoural lesions have not been already localized; it should be the first imaging modality in patients with gastro-enteropancreatic tumours: its initial use will result in more information and proper management.