The clinicopathological features, chromoendoscopic findings, and natural history of hamartomatous polyps of the stomach were compared with those of gastric hyperplastic polyps. Hamartomatous polyps were found significantly more frequently in adult females than adult males, and all were found significantly more frequently in adult females than adult males, and all were located in the gastric body or the fundus. In general, the number of polyps per patient was less in older patients. Histologically, all these polyps were formed of cystically dilated oxyntic glands and irregularly deformed oxyntic glands. Chromoendoscopic examinations using Congo red showed that the polyps were associated with extensive acid-secreting areas, were all located in acid-secreting areas, and had an acid-secreting function. Colonoscopy and/or radiologic examinations showed that one or a few polyps were frequently also present in the colons of these patients, but none of the families of the patients had a history of gastrointestinal polyposis. One to 11 years after the initial endoscopy, in seven (50.0%) of 14 patients with hamartomatous polyps followed up, the number of polyps decreased significantly.