The University of North Carolina (UNC) EoE clinico-pathologic database was used for this study. This database contains clinical, endoscopic, and pathologic characteristics on over 1,200 patients with esophageal eosinophilia from any cause from 2000 to 2007. It also contains information on patients in whom esophageal eosinophilia was excluded with a normal esophageal biopsy. Because this study was designed primarily to test reliability of determining eosinophil counts, subjects were selected based on their initial eosinophil counts (eos/hpf) performed for clinical care, and specifically chosen to represent a wide range of esophageal eosinophil counts, from 0 to >300 eos/hpf. The esophageal eosinophilia could have been from any cause, including EoE or gastroesophageal reflux disease, and clinical characteristics were not relevant for the purposes of this study. After identification of appropriate patients, archived pathology slides were pulled for review. This study was approved by the University of North Carolina Institutional Review Board.