Previous studies have suggested that patients with Barrett's oesophagus may be at increased risk of colorectal neoplasia, though the association is disputed. In a multicentre prospective study we compared the prevalence of colorectal adenomas in patients with Barrett's oesophagus and controls. Barrett's oesophagus patients (n = 104) had histological confirmation of columnar epithelium extending more than 3 cm above the gastro-oesophageal junction. The 537 controls were patients with symptoms suggesting irritable bowel syndrome. No participant had a personal history of colonic neoplasm. Each patient underwent colonoscopy. Histologically proven adenomas were found in 26 Barrett's patients (25%) and 75 controls (14%). Three colorectal cancers were discovered in each group. The prevalence of adenomas was greater in the Barrett's oesophagus group than in the control group (p < 0.01) but the relation became non-significant after adjustment for age and sex and control for other known risk factors by a logistic regression model (odds ratio 1.4 [0.7-2.7]). The relative risk of adenoma was significantly higher in patients older than 59 than in younger patients (2.2 [1.3-3.5]) and in men than in women (3.4 [2.0-5.7]). Other factors contributing significantly to the risk of adenoma were a family history of colorectal cancer (2.3 [1.1-4.8]), rectal bleeding (2.1 [1.1-3.9]), previous colonic investigation (0.3 [0.1-0.7]), and complete as opposed to partial colonoscopy (6.4 [0.8-48.3]). We conclude that Barrett's oesophagus is not an independent risk factor for colorectal neoplasia and, therefore, is not, in itself an indication for colorectal screening.