The aim of this study was to examine the relationship between smoking and oesophageal high-grade dysplasia (HGD) or adenocarcinoma (AC) in a large cohort of patients with Barrett's columnar-lined oesophagus (CLO). A total of 1280 patients diagnosed with CLO and registered with the UK National Barrett's Oesophagus Registry were included. Data, including smoking habits, were collected from the patient's notes and development of HGD or AC noted. Analysis was performed with SPSS using logistic regression for calculation of odds ratios (ORs) for development of HGD/AC. Data on smoking habits were available in 956 (74.6%) patients. There was no significant difference between smokers and nonsmokers in mean age (P=0.877) or length of follow-up (P=0.359). There was a significant risk of HGD/AC in patients with any history of smoking compared with those who had never smoked (P<0.001, OR 2.81). Ex-smokers of 10 years or more remained at a significantly higher risk of HGD/AC compared with those who had never smoked (P=0.001, OR 3.37). Current smokers were not at a significantly higher risk of HGD/AC compared with ex-smokers (P=0.857) nor were those who smoked at least 20 a day compared with those who smoked fewer than 20 a day (P=0.632). In patients with CLO, smoking appears to be a significant risk factor for the development of severe dysplastic disease; however, we did not observe a dose-dependent effect of smoking on progression of disease.