A case of somatostatin and pancreatic polypeptide (PP) producing tumor of the pancreas is presented. A 65-year-old woman was admitted for the evaluation of the tumor in the right upper quadrant of the abdomen. Clinical abnormalities included diabetic glucose intolerance, pancreatic insufficiency and marked dilatation of gallbladder. Marked high concentration of plasma PP and low levels of plasma insulin and glucagon were observed before operation. Plasma insulin concentrations in response to oral glucose tolerance test and arginine infusion were markedly low. A large quantity of somatostatin (4,300 ng/g ww) as well as PP (1,340 ng/g ww) was detected in the tumor, and somatostatin cells and PP cells were determined by immunofluorescence studies. After operation, pancreatic insufficiency and glucose intolerance were improved, and the patient made a favorable progress.