Compared with findings in Western countries, the prevalence of reflux esophagitis in Oriental countries is estimated to be low. In this prospective study, we aimed to examine the proportion of reflux esophagitis in Japanese adults, as evaluated by endoscopy. Endoscopists were prospectively directed to grade esophageal mucosal breaks with esophagitis according to the Los Angeles Classification of Esophagitis in all subjects that underwent endoscopic examination. In total, 6010 subjects underwent endoscopic examination for evaluation of esophagitis grading from December 1996 to February 1998. The subjects included 4394 outpatients who were not receiving medication for gastrointestinal disease and 1616 subjects who visited the hospital for routine physical examinations. The overall proportion of esophagitis was 16.3%. Most of the subjects with esophagitis were classified as having grade A or B (proportion of grades A and B, 9.6% and 4.6%, respectively). The age-related proportion of esophagitis and of severe esophagitis (i.e., grades C and D) increased in females aged over 70 and in males aged over 80. Increased body mass index (partly due to decreased height caused by osteoporosis), and/or hiatal herniation, were related to the proportion of esophagitis in females aged over 70. These data indicated that reflux esophagitis is a common disease in Japan. However, severe esophagitis (grades C and D) is not common.