Fifty consecutive massively obese patients referred for gastroplasty operations were prospectively studied to determine the existence of gastroesophageal reflux disease by means of a standardized questionnaire, 24-hr ambulatory pH-metry, and endoscopy (27 females, mean age 48 years, range 38-57 years). These patients had a body mass index (BMI) of 42.5 +/- 5.2 kg/m2 and an actual weight of 125.5 +/- 17 kg. Heartburn and acid regurgitation was reported by 37% and 28%, respectively, mostly of a mild degree (22% and 20%). Dysphagia was reported by 2%, but none had odynophagia. No patient had any macroscopic esophagitis. The pH data were compared with those obtained in 29 age- and sex-matched, symptom-free, healthy controls (15 females, mean age 47.6 years, range 30-63 years). During ambulatory pH-metry, we recorded a predominance of daytime reflux (7.2 +/- 8.2% and total acid exposure of 5.3 +/- 6.4%) in the obese patients, but neither the weight, BMI, nor the waist-hip ratio were significantly correlated with any of the reflux variables. The pH data obtained from these patients did not, however, differ significantly from those recorded in the control population, although a somewhat lower daytime acid reflux was found in the latter group. These results suggest that massive overweight is not associated with an increased prevalence of gastroesophageal reflux disease.