The diagnosis of Barrett's oesophagus has traditionally relied on the identification of a 3-cm segment of endoscopically abnormal epithelium (columnar) in the distal oesophagus. More recently, the presence of intestinal metaplasia has become essential. The importance of the definition relates to the identification of the risk of cancer development. These factors are discussed in the context of the rising incidence of adenocarcinoma, and the relative contributions of endoscopists and pathologists in determining likely progression are explored. We also discuss the advances in endoscopic technology that may aid the endoscopist in predicting malignant progression.