Patients who have a diagnosis of Barrett's esophagus typically undergo surveillance endoscopy every 1-3 years with multiple biopsy specimens obtained to facilitate early detection of progression of IM to dysplasia (more severe precancerous changes) and adenocarcinoma. (Sampliner RE. Updated guidelines for the diagnosis, surveillance, and therapy of Barrett's esophagus. Am J Gastro 2002;97:1888-1895.) Progression of IM to low-grade dysplasia (LGD) indicates that cells exhibit more "cancer-like" architecture, thus warranting an accelerated surveillance endoscopy and biopsy program every 6 months rather than every 1-3 years as indicated for non-dysplastic IM. Progression to high-grade dysplasia (HGD) indicates that the cells are even more "cancer-like", thus warranting an even higher frequency surveillance endoscopy and biopsy program (every 3 months). Many HGD patients may undergo photodynamic therapy (PDT) or surgical esophagectomy, rather than remain in a frequent surveillance program. This more aggressive therapy is warranted because of the high rate of progression of HGD to adenocarcinoma.