A number of previous studies have reported patients with Barrett's columnar metaplasia who have an increase or decrease in segment length over time. It is not clear whether patients who have an apparent shortening of the metaplastic segment are subsequently at a lower neoplastic risk and those whose segment length appears to increase are at a higher risk of adenocarcinoma development. The aim of this study was to investigate these issues by studying a large cohort of patients from the UK National Barrett's Oesophagus Registry. Medical records of 1533 patients registered with the UK National Barrett's Oesophagus Registry were examined from seven UK centers. Data were extracted on metaplastic segment length at surveillance endoscopies and histological findings on biopsy. Overall changes in segment length, variability in measurement and probability of the development of dysplasia and neoplasia over time were examined. At least two segment lengths were measured in 763 patients. The median change from measured diagnostic length to most outlying measured segment length was 3.0 cm, but overall there was no tendency for segment length to increase or decrease in the majority of patients with a follow up of up to 20 years. Most patients were treated with proton pump inhibitors. One hundred and eighty-six patients had three or more segment lengths over the first 10 years of follow up. No change in risk was demonstrated in these patients where length appeared to consistently increase with time or when it appeared to decrease. Overall, metaplastic columnar-lined esophagus segment length does not change over time, and when an apparent change is observed, this does not influence a risk of dysplasia or adenocarcinoma.