Barrett's oesophagus (BO), or replacement of the squamous mucosa by a specialized intestinal metaplasia due to gastro-oesophageal reflux disease (GORD), predisposes to adenocarcinoma. It is estimated that 6 to 12% of patients undergoing GI endoscopy have short BO (< 3 cm), and 1% have a long BO. Macroscopic diagnosis of BO is sometimes difficult and, in case of doubt, endoscopy should be redone after a period of efficient anti-secretory treatment. Diagnosis of BO is histological and should be confirmed by biopsies. The incidence of adenocarcinoma is globally estimated at 0.5% patient by year of follow-up, and exists for both short and long BO. Due to this low incidence, screening for BO is only justified in patients at high risk for adenocarcinoma (male gender, age > 50 ans, old GORD in a young patient). Low-grade dysplasia (LGD) then high-grade dysplasia (HGD) precedes adenocarcinoma. Histological diagnosis of LGD is difficult: the main cause of confusion is inflammation so diagnosis of LGD must be confirmed after a 3-month high-dose anti-secretory treatment. Diagnosis of HGD is easier but multiple biopsies are needed to determine the focal or multifocal disposition of HGD. The benefit of follow-up of BO is debated. Aged patients should be followed only if dysplasia is present. When dysplasia is absent, an endoscopic control with biopsies is desirable within 3 to 5 years. In case of dysplasia, the latter must be confirmed by another examination of biopsies, particularly in case of suspicion of HGD and after antisecretory treatment. In case of LGD, endoscopy with biopsies should be redone 6 months later to screen for HGD, then every year if LGD is confirmed. In case of HGD, the 5-year risk of cancer is 60% so surgical or endoscopic treatment is usually proposed. If HGD follow-up is decided, it should be performed on a 3- to 6-month basis.