We report a pancreatic endocrine tumor arising within an otherwise benign pancreatic serous cystadenoma in a 47-year-old woman with a history of lupus treated by steroids. She presented 10 years before resection with epigastric pain and intermittent jaundice. Histologic and immunohistochemical studies showed that the solid endocrine component was composed of small, uniform cells with stippled nuclei, which were chromogranin A positive. The surrounding cystic component was lined by periodic acid Schiff's-positive, diastase-digestible cells containing glycogen. To the best of our knowledge, this is the first case of a serous cystadenoma of the pancreas that contains a well defined pancreatic endocrine tumor reported in the English literature.