Adenomatous polyps have been well known to be premalignant, but it is still controversial how to treat and follow them up. Up to date, endoscopic resection has been the choice of treatment, particularly exceeding 2 cm, though there is no concensus on the indications for the excision of hyperplastic polyps. The incidence of malignant tissue found in hyperplastic polyps has been reported to be less than 3%, which is considerably lower than the incidence of greater than 6% reported in adenomas. There have been few reports of hyperplastic polyps in which malignant changes developed during endoscopic surveillance. We report a case of hyperplastic gastric polyp with intramucosal, well- differentiated adenocarcinoma with reviewing references. (Korean J Gastrointest Endosc 2004;28:188192)