Gastric dysplasia is generally accepted as a precancerous lesion. Ninety-nine patients with an initial diagnosis of gastric dysplasia, based on examination of endoscopic biopsies taken because of symptoms of dyspepsia, were followed to define the magnitude of the neoplastic risk. The degree of dysplasia in the initial biopsy was mild in 73 cases, moderate in 16, and severe in 10. Mild dysplasia was no longer detected in 74% of patients, persisted in 19%, and progressed in 7% (in four cases, to carcinoma). Moderate dysplasia regressed to mild dysplasia in 31% of cases, it was no longer found in 56%, and progressed to cancer in 13%. Our data show that both lesions can progress slowly, although in most instances they remain stable or regress. Thus, annual endoscopic and histologic controls appear to be advisable. Severe dysplasia was no longer detected in 20% of cases, regressed to moderate in 10%, persisted in 10%, and progressed to cancer in 60%; in half of these patients, carcinoma was detected within 3 months. Thus, severe dysplasia indicates a high risk of cancer, often a synchronous one, and it requires gastrectomy when it persists in repeated biopsies.