It is unknown which factors determine the severity of mucosal damage in gastroesophageal reflux disease (GERD). Our aim was to test whether the amount of esophageal acid exposure could predict the severity of esophageal injury in erosive reflux esophagitis. A total of 644 outpatients with symptomatic GERD underwent an esophagogastroduodenoscopy followed by esophageal manometry and 24-h pH monitoring. GERD was graded according to the endoscopic severity of mucosal damage as no erosions, single erosions, confluent erosions, esophageal ulcers, and strictures. A multiple linear regression was used to assess the joint influences of demographic characteristics, social habits, endoscopic anatomy, and various parameters of esophageal function tests on the severity of erosive reflux disease. No clear-cut association between the amount of acid reflux and the severity of erosive reflux esophagitis could be established. All individual parameters of esophageal pH monitoring, such as upright or supine acid contact time, frequency of all or only long reflux episodes, and an overall summary score of pH-metry, revealed no or only a weak correlation with the severity grade of erosive reflux esophagitis. Similarly, the pressure of the lower esophageal sphincter was only slightly more decreased in patients with extensive erosive esophagitis as compared to subjects without esophageal erosions. In the multiple linear regression, the presence of hiatus hernia was a stronger predictor of disease severity than any of the other parameters. In conclusion, factors other than exposure of the esophageal mucosa to acid must contribute to the development of erosive esophagitis.