To evaluate the clinical and biological significance of gastric dysplasia, we reviewed the histology of all available specimens of gastric mucosa in 85 patients in whom dysplasia had been previously diagnosed. The initial diagnosis of dysplasia was mild (Dy I) in 23 cases, moderate (Dy II) in 41 cases, and severe (Dy III) in 21 cases. The length of follow-up varied from 3 months to 11 years, with an average of 42 months. The follow-up of cases with Dy I and Dy II suggests that both lesions progress slowly and in most instances will remain stable or regress. In 18 cases, a carcinoma was found--17 in the group of Dy III and one in the group of Dy II. Of the 18 carcinomas, nine were at an early stage. Our data suggest that severe dysplasia is a reliable marker of high risk of gastric cancer and represents a strong indication for a gastrectomy.