High grade dysplasia of the gastric mucosa: a marker for gastric carcinoma. The natural history of gastric epithelial dysplasia and its relation to gastric cancer are ill defined. A consecutive series of 40 patients with an initial diagnosis of gastric epithelial dysplasia based on examination of endoscopic biopsies has been reviewed to determine the clinical outcome and to evaluate a two tier histological grading system as a predictor of the risk of cancer. On review, only 20 of the 40 patients were considered to have true dysplasia: seven patients had low grade dysplasia and 13 had high grade dysplasia. Of the 13 patients with high grade dysplasia, 11 (85%) were found to have gastric cancer within 15 months. Of the 10 patients with high grade dysplasia who underwent gastrectomy, six were found to have early gastric cancer, three had cancer invading into the muscularis propria, and none had lymph node metastases. High grade dysplasia is thus a marker of gastric cancer. Moreover, the cancers associated with high grade dysplasia are usually pathologically favourable and curable. The finding, by an experienced pathologist, of high grade dysplasia in two separate sets of endoscopic biopsies is therefore an indication for radical surgical treatment, provided that the patient's age and general condition permit such an approach. 