In Barrett's esophagus, the squamous lining of the lower esophagus is replaced by columnar epithelium. Barrett's esophagus is associated with gastroesophageal reflux and an increased risk of the development of esophageal cancer. Endoscopy shows red columnar epithelium in the lower esophagus. Biopsy is needed to confirm intestinal metaplasia. Some cases progress from dysplasia to invasive adenocarcinoma. Medical or surgical antireflux treatment controls symptoms and esophagitis, but Barrett's esophagus remains. Patients are usually followed up by endoscopy for detection of dysplasia or early cancer. For patients with low-grade dysplasia, follow-up is adequate; however, for those with high-grade dysplasia, esophagectomy or experimental endoscopic mucosal ablation is advised.