Barrett's oesophagus is associated with an increased risk of oesophageal adenocarcinoma. In 1985, Sontag et al reported an association between Barrett's oesophagus and colorectal cancer. This association has become controversial owing to conflicting evidence. Two recent papers indicate that although the prevalence of colon adenomas is the same in persons with Barrett's oesophagus as in the rest of the population, patients have an increased risk of developing colon cancer. A biologically plausible hypothesis is presented which explains the predisposition to both oesophageal and colon cancers. This hypothesis discusses the contribution of environmental factors such as alcohol, smoking and diet. In addition, it is proposed that the increased expression of the cyclo-oxygenase 2 enzyme is central to the predisposition to both oesophageal and colon cancers. Since this enzyme is inhibited by non-steroidal anti-inflammatory drugs such as aspirin and sulindac, these drugs hold promise as cancer chemopreventive agents in Barrett's oesophagus patients. Sulindac is the most promising of these agents owing to its efficacy in regressing colon polyps in patients with familial adenomatous polyposis.