Somatostatinomas are extremely rare endocrine tumors, and those with diameters above 2 cm are reported to increase the risk of metastasis significantly. We report a case of a large functional somatostatinoma in the pancreatic tail without metastases. A 46-year-old woman with a history of recurrent mild upper abdominal pain and diarrhea for 10 months was admitted to our hospital. Multiple-phase spiral computed tomography revealed a 10 cm x 8 cm, ill-defined, elliptic mass in the body and tail of the pancreas. There was a slightly heterogeneous enhancement on hepatic arterial phase and isodensity to the pancreatic parenchyma with small dotted necrosis within the middle region of the mass on hepatic portal venous and parenchymal phase, with patent splenic vein, dilated collaterals at the splenic hilum and no dilated pancreatic duct, resembling a diffuse infiltration tumor. To the best of our knowledge, this is the first description of multiple-phase spiral computed tomography findings of a functional somatostatinoma in the pancreatic tail and the largest thus far on reported computed tomography, with some differences compared with the previous reports.