Barrett's esophagus is a medical condition in which the squamous mucosa that normally lines the distal esophagus is replaced by a columnar type of epithelium. Most definitions that have been used for inclusion of patients in studies have indicated that columnar mucosa must extend 3 cm or more above the gastroesophageal junction. The precise length refers to the distance above the manometrically defined lower esophageal sphincter. This measurement is somewhat cumbersome to make on a routine basis for all patients at the time of endoscopy and thus is generally not done. It is important to realize that the gastroesophageal junction can be visually identified at the area where the esophagus tapers, in the region of the lower esophageal sphincter. The tapering of the esophagus in the region of the lower esophageal sphincter may be difficult to determine when lower esophageal sphincter pressures are low; thus, we commonly say that Barrett's esophagus is defined as columnar mucosa 3 cm above the region where the gastric folds end.