Barrett's esophagus (sometimes called Barrett's syndrome, CELLO, columnar epithelium lined lower (o)esophagus or colloquially as Barrett's) refers to an abnormal change (metaplasia) in the cells of the lower end of the esophagus thought to be caused by damage from chronic acid exposure, or reflux esophagitis. Barrett's esophagus is found in about 10% of patients who seek medical care for heartburn (gastroesophageal reflux). It is considered to be a premalignant condition and is associated with an increased risk of esophageal cancer.

The condition is named after Dr. Norman Barrett (1903-1979), Australian-born British surgeon at St Thomas' Hospital, who described the condition in 1957.