A duodenal ulcer is a sore that forms in the lining of the duodenum. Your duodenum is the first part of your small intestine, the part of your digestive system that food travels through straight after it leaves your stomach.
You can get an ulcer in your stomach as well as in your duodenum. Stomach ulcers and duodenal ulcers are both types of peptic ulcers. If you have either of these, you have what’s called ‘peptic ulcer disease’.