A gastroscopy is a test where an operator – a doctor or nurse – looks into the upper part of your gut (the upper gastrointestinal tract).
The upper gut consists of the gullet (oesophagus), the stomach and the first part of the gut (small intestine) known as the duodenum. The operator uses an endoscope to look inside your gut. Therefore, the test is sometimes called endoscopy.
An endoscope is a thin, flexible telescope. It is about as thick as a little finger. The endoscope is passed through the mouth, into the oesophagus and down towards the stomach and duodenum.