20 Background: Esophageal adenocarcinoma (EAC) incidence is rising and prognosis is uniformly poor, even with early stage disease. Barrett esophagus (BE) serves as a premalignant marker for EAC, with an estimated progression of 0.5% per year. Low-grade (LGD) and high-grade dysplasia (HGD) confer a higher risk of progression, providing an opportunity for intervention and surveillance. Aims: To evaluate a large cohort of patients undergoing endoscopic evaluation of BE and thereby better understand the natural history of BE and dysplasia. Methods: A retrospective review of endoscopic databases was conducted for all patients with the diagnosis of BE undergoing upper endoscopy at a tertiary academic medical center from 1991-2010. All endoscopy and accompanying pathology reports were reviewed. Only those patients with 2 biopsies documenting specialized intestinal metaplasia were analyzed. Results: 848 patients underwent upper endoscopy for evaluation of BE. Of these, 674 patients met inclusion criteria, at a mean follow up of 66.6 months. Table 1 depicts the distribution of patients according to their histology at presentation. 22 (3.2%) patients presented with established EAC, while EAC developed in 51 (7.6%). Of patients with HGD, LGD, or no dysplasia (ND) at presentation, EAC ultimately developed in 30.6%, 6.6%, and 2.7%, respectively. EAC developed in 4 patients despite RFA treatment for ND (2) or LGD (2). HGD developed in 6 such patients after treatment for ND (3) and LGD (3). Only 1 patient in each RFA-treated cohort required esophagectomy, while the others cleared dysplasia or EAC with continuous treatment. Conclusions: In this large cohort of patients with Barrett’s esophagus, higher grade of dysplasia at first endoscopy was associated with development of EAC. Continuous surveillance during and after endoscopic treatment is necessary and often results in clearance of dysplasia and EAC. [Table: see text]