In previous studies, increasing body mass index (BMI, kg/m(2)) was related to chronic gastrointestinal symptoms, such as frequent vomiting, upper abdominal pain, bloating and diarrhea. However, there have been no reports about the relationship between increasing BMI and abnormal upper endoscopic findings such as gastritis or ulcer. The study group consisted of 27 319 individuals who underwent medical checkup at a healthcare center from 1 January to 31 December 2003. The following classification of BMI was applied. (i) underweight; BMI < 18.5; (ii) normal weight; 18.5 <or= BMI < 25.0; (iii) overweight; 25.0 <or= BMI < 30.0; and (iv) obese; BMI >or= 30.0. The subjects were grouped according to the findings of upper endoscopy as follows: group 1, those with erosive gastritis, gastric ulcers (benign and malignant) and duodenal ulcers; group 2, those with reflux esophagitis; and group 3, those with findings of upper endoscopy other than group 1 and group 2. The prevalence of obesity and overweight was 2.2% and 30.5%, respectively. By multivariate analyses, overweight (OR 1.31, 95% CI; 1.22-1.40, P = 0.000) and obesity (OR 1.40, 95% CI; 1.14-1.72, P = 0.001) were significant contributors of group 1. Overweight (OR 1.61, 95% CI; 1.42-1.83, P = 0.000) and obesity (OR 2.23, 95% CI; 1.59-3.11, P = 0.000) were also significant contributors of group 2. In the general population, increasing BMI was associated with abnormal upper endoscopic findings, such as erosive gastritis, gastric ulcer, duodenal ulcer and reflux esophagitis. Clarification of the cause-and-effect relationships and the mechanisms of these associations require further investigation.