Twenty-five cases of benign giant duodenal ulcer have been studied. In every case a barium meal examination showed an ulcer crater with a radiographic diameter of at least 2 centimetres. Abdominal pain was the commonest symptom but less than half of the patients had had pain characteristic of chronic peptic ulcer. Haemorrhage from the ulcer occurred in a large majority of them. The radiological appearances are described, and it has been shown that the giant ulcer may be missed through being mistaken for the duodenal cap or else misdiagnosed. It appears that the death rate in this condition has been falling but it is still high. The management of patients with giant ulcers is discussed.