Barrett esophagus is a condition in which the lining of the esophagus (the tube that connects the mouth to the stomach) becomes abnormal. This change may occur when stomach contents, including acid, rise up into the esophagus, a condition known as gastroesophageal reflux disease (GERD). The only way to know if a person has Barrett changes is to look at the esophagus with a special instrument that is passed through the mouth into the esophagus and stomach (a procedure called esophagogastroduodenoscopy, or EGD). Using this instrument, the doctor can also take samples of the esophageal lining to examine under a microscope. Most people who have GERD never develop Barrett esophagus, but those who do are at a higher risk for esophageal cancer. Many experts therefore recommend that people with Barrett esophagus get EGDs regularly to catch cancer in an early, more treatable stage. It has been thought that the greater the length of the esophagus that shows Barrett changes, the greater the chances of developing esophageal cancer, but this has never been shown for certain.