Upper gastrointestinal (UGI) endoscopy is a test that allows the doctor to look at the interior lining of the upper digestive tract (the esophagus, stomach, and upper end of the small intestine) through a thin, flexible viewing instrument called an endoscope. The tip of the endoscope is inserted through the mouth and then gently advanced down the throat into the esophagus, stomach, and upper small intestine (duodenum).

Through the endoscope, the doctor can look for ulcers, inflammation, tumours, infection, or bleeding. Tissue samples can be collected (for biopsy), polyps can be removed, and bleeding can be treated through the endoscope. Endoscopy can reveal problems that do not show up on X-ray tests and can sometimes eliminate the need for exploratory surgery.