The incidence of patients with gastric carcinoma having had a previously diagnosed or suspected peptic ulcer was noted in two studies. These studies were the West Midlands Gastric Chemotherapy Trial (1974--6) and a retrospective study of patients presenting to the United Birmingham Hospitals with gastric carcinoma during the years 1958--62 and 1968--72. The incidence of patients found to have had a previous operation for duodenal ulcer or to have post-mortem evidence of one was 6.5 per cent and 5.7 per cent respectively. A radiologically proved duodenal ulcer had been identified in 5.5 per cent and 2.1 per cent respectively and the incidence of previous symptoms suggestive of a duodenal ulcer was 4.0 per cent and 5.2 per cent. These figures indicate the total incidence could be 12.97--16.0 per cent, which is much higher than previously reported. The mean time interval between operation for duodenal ulcer and the development of gastric carcinoma was much longer in patients having had a partial gastrectomy than in patients having had a vagotomy and drainage procedure. The incidence of previous benign gastric ulcers was 2.5 per cent and 0.9 per cent. Fifty-three per cent of patients having had a previous operation for duodenal ulceration were found to have an unresectable carcinoma, compared with the overall unresectable rate of 35 per cent.