BACKGROUND: Morbid obesity has long been considered as a contributing factor to gastro-esophageal reflux, but the literature contains conflicting data on the subject. The authors studied a large number of morbidly obese candidates for bariatric surgery with objective means, in order to better define the incidence of gastro-esophageal reflux disease (GERD) and esophageal motility disorders in this population. METHODS: Morbidly obese patients, in whom indication for bariatric surgery was confirmed after complete evaluation, were included consecutively during a 4-year period. The evaluation included history of reflux symptoms, upper GI endoscopy, 24-hour pH monitoring, and stationary esophageal manometry. RESULTS: 345 patients were studied, of whom 35.8% reported reflux symptoms. Endoscopy showed a hiatus hernia in 181 patients (52.6%), and reflux esophagitis in 108 (31.4%). 24-hour pH monitoring revealed an elevated De Meester score in 163 patients (51.7%). Manometry was normal in 247 patients (74.4%), and showed a decreased lower esophageal sphincter pressure in 59 (17.7%). Esophagitis and abnormal pH testing were more common in patients with symptoms or hiatus hernia, and the incidence of esophagitis was higher with abnormal pH testing. Esophagitis was associated with increased weight and abdominal obesity. CONCLUSIONS: This study confirms the increased prevalence of GERD in the morbidly obese population. Upper GI endoscopy should be performed routinely during evaluation of morbidly obese patients for bariatric surgery. When both conditions coexist, effective treatment is probably best provided by Roux-en-Y gastric bypass, which produces effective weight loss and correction of pathological reflux.