Six-hundred-and-ninety-four patients with localized gastric lesions (ulcers, polyps, enlarged or irregular folds, erosions and tumors) underwent endoscopic examination and multiple biopsies. Twenty-nine proved to have severe or moderate gastric epithelial dysplasia. Another group of 123 patients were submitted to endoscopic examination and multiple biopsies, but showed no evidence of localized gastric lesions. Only one case of mild dysplasia was observed in this group. Of the 29 patients with dysplasia, 8 (27.5%) had a carcinoma in the surgical specimen. The endoscopic follow-up carried out in non-operated patients with dysplasia did not show any development of malignancy. This study shows dysplastic changes significantly associated with prominent or depressed lesions of the gastric mucosa at endoscopy. In operated patients a synchronous carcinoma is often detected in the surgical specimen.