Endoscopy and biopsy of the upper gastrointestinal tract and terminal ileum were performed in 24 patients with familial polyposis or Gardner's syndrome in order to further define the incidence of extracolonic adenomatous polyps. Polyps, usually multiple and small in size, were detected in the gastric fundus (12.5 percent), antrum (29.1 percent), duodenum (66.6 percent), and terminal ileum (41.7 percent). Histology showed hyperplasia of the fundic glands and cystic dilatation in the polyps of gastric fundus, and adenomas in several cases of antral (three patients) or duodenal polyps (14 patients). Polyps of the terminal ileum were either adenomas (five patients) or lymphoid aggregates. Patients with stigmata of Gardner's syndrome, desmoids or mesenteric fibromatosis presented a major incidence of adenomas in the duodenum, but not in other parts of the digestive tract investigated. Subsequent checkup after an average of 33 months in ten patients revealed an increase of lesions only in the duodenum in two patients. These findings confirm that adenomatous polyps are not limited to the colon and rectum, as previously believed, but can affect the whole gastrointestinal tract. Periodic surveillance of mucosa seems to be indicated, especially for the duodenum, since degeneration of adenomas into carcinoma is possible.