This endoscopic evaluation of 25 patients with familial polyposis coli (FPC) further establishes gastro-duodenal polyps as a significant extracolonic manifestation of the condition. Ten patients had polyps, distributed as follows: stomach (2), duodenum (4), stomach and duodenum (4). Altogether, there were six gastric and seven duodenal lesions. Half of the gastric tumors were hyperplastic and half were adenomatous. All the duodenal tumors were adenomatous, four being ampullary. The one symptomatic patient had intra-polypoid adenocarcinoma. There were no significant correlations between the endoscopic findings and patient age, sex, presence of colon cancer, or other extracolonic abnormalities. The authors affirm that gastroduodenal polyps are an important component of FPC and recommend that all patients with this condition undergo initial and follow-up gastroduodenoscopy. Multiple small lesions may be carefully monitored, but larger ones, particularly those in the region of the ampulla, must be excised.