It is well known from the older literature that gastric carcinomas are more likely to develop in a stomach containing hyperplastic polyps. The reason why such a stomach should represent a precancerous condition is, however, largely unexplained. The aim of this study was to determine the disorders of the gastric mucosa in which hyperplastic polyps occur. In 244 patients with hyperplastic polyp, in whom at least two additional biopsies each from the antrum and corpus were available, gastritis was classified on the basis of the updated Sydney System. In none of the 244 patients was the gastric mucosa found to be normal. The most common disorder, at 51.3%, was autoimmune gastritis of the corpus mucosa, while chronic active Helicobacter pylori (Hp) gastritis was seen in 37.3% of the patients. Of the patients with Hp gastritis, 56.1% had corpus-dominant Hp gastritis. Other forms were relatively rare: when A-gastritis, corpus-dominant Hp gastritis and any other form of Hp gastritis were lumped together as a precancerous condition, these changes were found in 88.6% of the patients with hyperplastic polyps of the stomach. In the presence of hyperplastic polyps of the gastric mucosa, additional biopsies obtained from the antrum and corpus should always be performed to obtain a basis for deciding whether to apply Hp eradication treatment as potential carcinoma prophylaxis.