High numbers of high-affinity somatostatin binding sites have been found on carcinoid tumors, gastrinomas, small cell lung cancers and the majority of medullary thyroid cancers, enabling in vivo visualization of these tumors with octreotide scintigraphy. A comparison of the results obtained at our institution and another 15 centers in Europe show a few remarkable similarities and differences. The overall sensitivity of octreotide receptor scintigraphy to detect the primary GEP tumor and its metastases is high, e.g. 80-90%. The main difference was found in gastrinomas and to a lesser extent in insulinomas. These differences might be attributed to different scanning protocols. Furthermore, octreotide scintigraphy also has a high sensitivity to localize the primary tumor and its metastases causing Cushing's syndrome by ectopic production of ACTH or CRH. Octreotide scintigraphy is a new, sensitive and noninvasive technique to localize somatostatin receptor expressing endocrine tumors and their metastases.