Endoscopy constitutes an important investigation in the presence of a gastro-oesophageal reflux. The primary intention is to exclude the possibility of an organic pathology, for example cancer, which has not been demonstrated by other investigative procedures. Accordingly it must provide a detailed exploration of the whole superior digestive tract, from the mouth to the duodenum. Secondly, endoscopy must establish the consequence of the reflux on the mucosa of the lower oesophagus both by a macroscopic and a detailed microscopic description. Peptic lesions are classified according to 4 degrees of severity. The difficulty in evaluating the very early lesions (1st degree) and the advanced stages (4th degree) necessitates systematic biopsies of the lesions. The erythroplasic type of carcinoma in situ can present the same endoscopic changes as a 1st degree peptic lesion, whereas the exclusion of an adenocarcinoma constitutes the major preoccupation at the time of endoscopy of a 4th degree oesophagitis.