Upper gastrointestinal endoscopy revealed gastroduodenal polyps in 45 (90%) out of 50 patients with familial adenomatosis (FA), and in 11 (92%) out of 12 patients with juvenile polyposis (JP). The polyps in the fundic and corpus regions of the stomach were hamartomatous cystic body gland polyps in 28 (56%), and adenomas in 3 (6%) of the FA patients, while 6 (50%) JP patients had hyperplastic polyps in the corresponding region. The polyps in the gastric antrum and duodenum were adenomas in 6 (12%) and 25 (50%) of the FA patients, respectively, while the polyps of the corresponding regions were hyperplastic in 10 (83%) and 2 (17%) of the JP subjects. One focal adenomatous lesion in an antral hyperplastic polyp, and one duodenal adenoma were found in the JP patients. Furthermore, one duodenal adenocarcinoma was observed among the FA subjects. It is concluded that gastroduodenal polyps belong inherently both to adenomatous and to juvenile varieties of gastrointestinal polyposis, and that these two conditions have characteristic histological patterns and topography of polyps in the upper gastrointestinal tract.