A 66-year-old woman had been receiving follow-up since 1990 for hyperplastic polyposis, which remained unchanged endoscopically and radiologically. In 1999, a small (28 x 22 mm) superficial adenocarcinoma was detected in the ascending colon. Histologically, this was a hyperplastic polyp containing a well-differentiated adenocarcinoma invading into the submucosa. A review of the English and Japanese literature identified 32 cases of "hyperplastic polyposis." In about half of the 32 cases, an adenocarcinoma was also found amongst the hyperplastic polyps. Half of the adenocarcinomas were located in the right colon. Although hyperplastic polyposis is uncommon, it warrants regular surveillance, as it appears to be associated with an increased risk of colorectal cancer.