Endoscopy and biopsy of the terminal ileum were performed in 18 patients with familial adenomatosis coli/Gardner's syndrome. All had undergone total colectomy with ileoproctostomy 7 to 249 months (average, 79.7 months) before the study. In all of these patients, endoscopic studies revealed multiple or innumerable small (less than 4 mm in diameter) polypoid lesions, all recognizable as whitish, sessile elevations. Histologic findings of the biopsy specimens from the polypoid lesions showed tubular adenoma, with or without lymphoid hyperplasia, in nine (50 percent), but only lymphoid hyperplasia in the other nine patients. Colonic metaplasia was present in the adjacent ileal mucosa in 3 patients with ileal adenomas. The incidence (83 percent) of ileal adenomas detected 113 to 249 months after colectomy was higher than that (33 percent) found 7 to 90 months after surgery. In view of these results, endoscopy and biopsy of the terminal ileum, as well as the retained rectum, should be done periodically for postcolectomy patients with this disease.