In 13 200 consecutive gastroscopies polyp-like lesions were found in 454 patients and of these 425 were examined histologically. Tumours other than polyps were excluded and there remained 357 cases which were divided in four groups: adenoma (8%), hyperplastic polyp (34%), foveolar hyperplasia (21%) and inflammatory polyp (36%). Transitional forms between different groups were seen and sometimes characteristics of different polyptypes could be seen within one and same polyp. In addition, the mean age of the patients increased in order: inflammatory polyp, foveolar hyperplasia, hyperplastic polyp and adenoma, suggesting that the different groups are not separate entities but represent related stages in the morphogenesis of gastric polyps. 219 cases out of 357 patients were re-examined endoscopically on average 2.5 years after the first examination. This examination revealed new polyps in 26% of all cases and spontaneous disappearance of the polyps in 14% of cases suggesting that gastric polyps, particularly those of the hyperplastic and inflammatory type are in a dynamically labile state. Gastric carcinoma was found in 27 (8%) of patients with polyps. In 4 of these cases the carcinoma was found at the re-examination (which in 3 cases was performed within 0.5 and in 1 case within 1.5 year). In 14 cases carcinoma was found inside the polyps and in 6 of these carcinoma was "early" in its growth. In 13 cases carcinoma was found outside the polyps and in all of these carcinoma was "advanced". Carcinoma was found in 38% of adenoma cases and in 5% of cases with polyps other than adenomas.