A total of 32 histologically documented cases of heterotopic pancreas was found in a review of the records of the department of pathology at the Chang Gung Memorial Hospital between 1977 and 1987. This review was done to ascertain the clinical significance of this uncommon entity. In 14 patients (44%), the aberrant pancreatic tissue was symptomatic; in the other 18 (56%), it was found incidentally. In the symptomatic group, the heterotopic pancreatic tissue was found in a duplication cyst of the ileum in one patient, in the common bile duct in one, in a Meckel's diverticulum in four, in the stomach in three, in a congenital duodenal diaphragm in one, in the duodenum in three, and in the ileum in one. The majority of heterotopic pancreatic tissue in the asymptomatic group was encountered in the jejunum (15 patients). Symptoms were related to complications, including obstruction of the common bile duct, mucosal ulcer with hemorrhage, intussusception, and intestinal obstruction, but not to pathologic conditions of the pancreas itself, such as pancreatitis or pancreatic cyst or neoplasm. In all of the clinically significant cases, the clinical symptoms disappeared completely after surgical removal of the aberrant tissue. In 28 cases (87%), diagnosis was made by frozen section during operation. Preoperative diagnosis of aberrant pancreas was not made in any of the cases. Histologically, all cases showed pancreatic excretory ducts; in 31 cases (97%), exocrine glands were present, and in 27 cases (84%), islets of Langerhans were discernible. There was no relationship between symptoms and the presence of islets, acini, or ducts. Mallory's phosphotungstic acid-hematoxylin stain was used to demonstrate zymogen granules in the acinar cells, and insulin, glucagon, and somatostatin were demonstrated with the horseradish peroxidase-antihorseradish peroxidase immunocytochemical staining technique; islets of Langerhans were also identified. Technetium Tc 99m scintigraphy was used to detect the bleeding source in a Meckel's diverticulum and an enteric duplication associated with ectopic gastric mucosa.