In two patients with functionally active, nonatrophic oxyntic gastric mucosa, hyperplastic polyps developed on the gastric side of Billroth II and Billroth I anastomoses. The polyp associated with the Billroth II procedure was almost circumferential, sparing only the lesser curvature. That associated with the Billroth I operation was on the anterior wall from lesser to greater curvature. The operations had been performed 11 years and ten years earlier for peptic ulcers of the gastroduodenal junction. The sites of polyp formation resembled those of experimental cancers in rats with Billroth I and Billroth II anastomoses, and of human cancer occurring 20 or more years after gastrojejunostomy for benign disease. This suggests that stomal carcinomas and hyperplastic polyps each result from the reflux of enteric contents into the stomach remnant.