Barrett's oesophagus is a precancerous condition in which the normal squamous epithelium is replaced by intestinal metaplasia (IM). IM can then progress through increasingly severe dysplasia to oesophageal adenocarcinoma (EAC). In the gastric cardia the normal gastric mucosa, when inflamed (carditis), can be replaced by IM and can then progress to gastric adenocarcinoma (GAC). The same histopathological sequence can take place on either side of the oesophagogastric junction. Since the location of that junction can be uncertain this can result in confused diagnosis between EAC and GAC. In this review, the diagnostic criteria, incidence and risk factors for Barrett's oesophagus and carditis are discussed, together with the factors determining the risk of progression to adenocarcinoma of the oesophagus or cardia. The risk factors include familial/genetic, environmental and dietary characteristics. Finally, these risk factors are discussed within the context of cancer prevention.