In June, 1993, a 55-year-old man was seen at the hospital because he felt an abdominal tumor. He had normal blood insulin and glucagon levels. Abdominal ultrasonogram (US), CT, magnetic resonance imaging (MRI), endoscopic retrograde cholangiopancreatography (ERCP) and angiography raised a suspicion of a pancreatic acinar cell carcinoma originating from the tail of the pancreas. An operation was done on July 26, 1994, and a dark red tumor was found to originate from the tail of the pancreas, involving the transverse mesocolon and greater omentum. Surgical resection of the body and tail of the pancreas, spleen, and left hemicolon, as well as lymph node dissection were performed. The histopathological diagnosis of the tumor was Glimelius stain-positive pancreatic endocrine tumor formed of dyskaryotic, strongly eosinophilic bodies. The immunohistochemical stainings for gastrin, insulin, glucagon, VIP, and calcitonin were negative, thus indicating no evidence of hormone production. Nevetheless, electron microscopic examination revealed fairly large endocrine granules in the cytoplasm of some cells of this tumor. The presence of somatostain cells derived from D-cells was sugested. Finally this tumor was diagnosed as nonfunctioning pancreatic endocrine tumor. A review of the relevant literature is also presented here.