Somatostatin is known to inhibit the secretory release of other peptide hormones. Somatostatinomas associated either with or without somatostatinoma (inhibitory) syndrome are rare neoplasms among gut-pancreatic endocrinomas. Collected from international literature, this study aimed to perform a statistical analysis on 173 patients with somatostatinoma/inhibitory syndrome. The evaluation further attempted to provide investigators in this particular field of research with extensive and precise information on the present situation of somatostatinoma. The 173 patients consisted of 81 with pancreatic somatostatinomas and 92 with extrapancreatic somatostatinomas. Most of the latter were found to have originated in the duodenum and may be termed as carcinoid somatostatinoma. Where data were considered to be adequate, a comparative study was carried out between two groups, pancreatic and duodenal, each consisting of 81 patients. A statistically significant difference between these two groups was found in the incidence of inhibitory syndrome (18.5% versus 2.5%) and von Recklinghausen's disease (1.2% versus 43.2%), large size of tumor (>20 mm) (85.5% versus 41.4%), multisecretory activities (33.3% versus 16.3%), and presence of psammoma bodies (2.5% versus 49.4%). There was no statistically significant difference in the rate of metastases and malignancy between the two groups. The average postoperative 5-year survival rate was 75.2% in 90 patients overall, 59.9% in 44 with metastases and 100.0% in 46 without metastases. Compared with the other pancreatic endocrinomas, including PPomas, glucagonomas, vipomas, gastrinomas, and insulinomas, somatostatinomas were characterized by the low rate of the relevant syndrome and multiple endocrine neoplasia syndrome type 1. There was a low rate of multiplicity, and a high incidence of psammoma bodies in the duodenal group particularly with von Recklinghausen's disease. A high rate of malignancy was recorded, resulting in a low postoperative survival rate of patients with metastases. In conclusion, somatostatinomas exhibited characteristic features quite different from those of the other pancreatic endocrinomas regarding multiple points.