Barrett's oesophagus or columnar lined epithelium of the oesophagus (CLO) is a metaplastic condition associated with excessive gastro-oesophageal reflux. It is found in 15% of patients with reflux oesophagitis. In a detailed study of 115 CLO patients dysplasia was found in 46%; 13.9% were moderate or severe dysplasia, usually found in intestinal type CLO. Fifty patients were endoscoped annually to determine the natural history of the disease. The incidence of adenocarcinoma was 1 in 52 patient-years, a 125-fold excess risk. A dysplasia-carcinoma sequence was seen in the five who developed carcinoma. Patients with early carcinoma were treated surgically with 12% postoperative mortality and 100% survival for 24-70 months.