A 50-year-old woman was admitted because of severe sideropenic anemia. The gastrin levels were within normal ranges. Esophagogastroduodenoscopy showed diffuse gastric polyposis with signs of diffuse oozing. Colonoscopy showed the presence of a 3-cm wide pedunculated polyp of the ascending colon, which was removed by diathermy. The patient was treated by total gastrectomy with Roux-Y esophagojejunostomy. Histological examination showed the presence of diffuse gastric polyposis with the contemporary occurrence of hyperplastic polyps and mixed hyperplastic and adenomatous polyps, with a tubular pattern and the focal aspect of serrate adenoma. This is the first case report of sporadic diffuse hyperplastic and adenomatous polyposis of the stomach.