Twenty-six giant duodenal ulcers, all correctly diagnosed prior to endoscopy, are presented. The concept of the ulcer/bulb ratio (ratio of longest diameter of the ulcer to that of the total bulb including the ulcer) is introduced. In all cases this ratio was 0.8 or greater; in 18 cases (69%) the ulcer completely replaced the duodenal bulb. An 'ulcer within an ulcer' appearance, representing a small area of deeper ulceration within the giant ulcer, was noted in 8 (31%). Half of the patients have remained symptom-free on medical therapy alone. Only two patients in our series (8%) died of complications of giant duodenal ulcer.