The development of gastric dysplasia and neoplasia in patients with pernicious anaemia has been evaluated in a prospective clinical and endoscopic follow up study. After initial screening of 80 patients between 1978 and 1980, one patient underwent total gastrectomy for a gastric malignancy and 12 were kept under surveillance and underwent endoscopy at a mean interval of 14 months. In the remaining 67 patients further investigation was attempted six to seven years after the initial investigation. The continuous follow up study identified carcinoids in one patient and an adenoma with severe dysplasia in a further patient. The grade and site of mucosal dysplasia differed from one investigation to the next, but no overall progression was observed. Of the 79 patients, eight had died by the time of the reinvestigation, two of unknown cause and six of causes unrelated to pernicious anaemia. In 38 of the remaining 71 patients, clinical data only were available, with no evidence of new gastric malignancy. In 27 patients it was possible to perform an upper gastrointestinal endoscopy, when no change in the degree of dysplasia was detected. In six patients no follow up information was obtainable. In conclusion, patients with pernicious anaemia should be investigated by upper gastrointestinal endoscopy soon after diagnosis. Polyps should be removed wherever possible. In the presence of severe mucosal dysplasia or polyps that are not removed, frequent reinvestigation should be performed, provided the patient is eligible for gastric surgery. In the remaining patients, follow up endoscopies at about five year intervals would seem sufficient.