Chronic gastro-oesophageal reflux might lead to the development of Barrett's oesophagus (BO) or even oesophageal adenocarcinoma. There has been no definitive systematic review and meta-analysis of data to estimate global prevalence of BO or oesophageal adenocarcinoma in individuals with gastro-oesophageal reflux.We searched MEDLINE, Embase and Embase Classic to identify cross-sectional surveys that reported prevalence of BO or oesophageal adenocarcinoma in adults with gastro-oesophageal reflux. We extracted prevalence for all studies, both for endoscopically suspected and histologically confirmed cases. We calculated pooled prevalence according to study location, symptom frequency and sex, as well as ORs with 95% CIs.Of the 4963 citations evaluated, 44 reported prevalence of endoscopically suspected and/or histologically confirmed BO. Prevalence of BO among individuals with gastro-oesophageal reflux varied according to different geographical regions ranging from 3% to 14% for histologically confirmed BO with a pooled prevalence of 7.2% (95% CI 5.4% to 9.3%), whereas pooled prevalence for endoscopically suspected BO was 12.0% (95% CI 5.5% to 20.3%). There was heterogeneity in many of our analyses. Prevalence of BO was significantly higher in men, both for endoscopically suspected (OR=2.1; 95% CI 1.6 to 2.8) and histologically confirmed BO (OR=2.3; 95% CI 1.7 to 3.2). Dysplasia was present in 13.9% (95% CI 8.9% to 19.8%) of cases of histologically confirmed BO, 80.7% of which was low-grade.The prevalence of Barrett's oesophagus among individuals with gastro-oesophageal reflux varied strikingly among countries, broadly resembling the geographical distribution of gastro-oesophageal reflux itself. Prevalence of BO was significantly higher in men.