The prevalence of gastroesophageal reflux disease (GERD) is increasing in Korea. Obesity, old age, hiatal hernia, and a high-calorie diet are generally known as risk factors for GERD. But not enough research has been done on the many factors affecting the diagnostic severity of endoscopic esophagitis. The purpose of this study was to evaluate the relationship between endoscopic findings and variable clinical factors in patients with GERD. A retrospective study was performed in 258 patients with heartburn or acid reflux symptoms who underwent endoscopy from January 2005 to April 2008 at Chonnam National University Hospital. Patients were classified in the ERD (erosive reflux disease) or NERD (non-erosive reflux disease) group depending on the presence of erosion. The risk of endoscopic esophagitis was analyzed with regard to several variables, such as symptom severity, age, BMI, presence of endoscopically suspected esophageal metaplasia (ESEM), smoking, alcohol, caffeine, exercise, Helicobacter pylori, lipid profiles, and use of hypnotics. The incidence of endoscopically suspected NERD was 59.3% (153 patients) and that of ERD was 40.7% (105 patients). Hiatal hernia was more frequent in the ERD group [30.1% (31/103)] than in the NERD group [15.7% (24/153); p=0.006]. Endoscopically suspected Barrett's esophagus was more frequent in the NERD group [23.5% (36/153)] than in the ERD group [13.6% (14/103); p=0.049]. Use of hypnotics was more frequent in the ERD group [14.9% (14/94)] than in the NERD group [8.7% (13/149); p=0.136]. By logistic regression analysis, erosive esophagitis was correlated with hiatal hernia [adjusted odds ratio (aOR)=2.70, 95% confidence interval (CI): 1.39~5.25, p=0.004] and use of hypnotics (aOR=2.50, 95% CI: 1.07~5.84, p=0.035). In GERD, risk factors for esophageal mucosal damage were hiatal hernia and sleep disturbance.