A well granulated beta cell adenoma of the pancreas was found incidentally at autopsy in a patient with a ruptured aortic aneurysm. The tumor was studied by histochemical an immunocytochemical methods. It consisted of a trabecular arrangement of insulin storing cells intermingled with small ducts. Both components were tightly contiguous. Goblet cells were also present within the tumor cell nests. The implication of the growth of the different types of cells is discussed in relation to the concept of an APUD system.