We performed this study to evaluate the prevalence of reflux esophagitis and/or hiatal hernia in patients referred to a medical center and to examine the relationship between endoscopic reflux esophagitis and hiatal hernia. The study was carried out in 1,010 patients referred to Yong Dong Severance Hospital for upper gastrointestinal endoscopy because of symptoms related to the gastrointestinal tract from September 1994 to March 1996. The presence of hiatal hernia was defined as a circular extension of the gastric mucosa of 2 cm or more above the diaphragmatic hiatus. Reflux esophagitis was found in 5.3% of patients, hiatal hernia in 4.1%, duodenal ulcer in 7.2% and gastric ulcer in 8.2%. The prevalence rates of reflux esophagitis and hiatal hernia in males were significantly higher than those in females. Thirty-two percent of patients with reflux esophagitis had hiatal hernia. In patients without reflux esophagitis, hiatal hernia was found in only 2.5% (p<0.01). There was no significant association between the presence of hiatal hernia and the degree of esophagitis on endoscopy. Duodenal ulcer was the second most common endoscopic abnormality found in patients with reflux esophagitis. The prevalence rate of reflux esophagitis and/or hiatal hernia at a medical center is relatively low compared to peptic ulcer disease and other reports from the Western countries. Our study confirms the close association between reflux esophagitis and hiatal hernia.