Although the etiology of gastroesophageal reflux disease (GERD) is multifactorial, the pathophysiology of the disease in morbidly obese patients remains incompletely understood. The aims of this study were to compare in morbidly obese (body mass index (BMI) > or =35) and nonmorbidly patients (BMI <35) with GERD: (a) lower esophageal sphincter (LES) profile; (b) esophageal body function; and (c) esophageal acid exposure. We reviewed esophageal manometry and ambulatory 24-hour pH monitoring studies of 599 consecutive patients with GERD (DeMeester score >14.7). Patients were divided into two groups according to the BMI: (1) 520 patients (86.8%) with BMI <35 and (2) 79 patients (13.2%) with BMI > or =35. While the DeMeester score was not different between the two groups, morbidly obese patients had higher LES pressure and higher amplitude of peristalsis in the distal esophagus (DEA). Among these patients, LES and DEA pressures were often hypertensive. A linear regression model showed that BMI, LES pressure, LES abdominal length, and DEA were independently associated with the DeMeester score. These data showed that: (a) BMI was independently associated to the severity of GERD; and (b) in most morbidly obese patients with GERD, reflux occurred despite normal or hypertensive esophageal motility. These findings show that the pathophysiology of GERD in morbidly obese patients might differ from that of nonobese patients, suggesting the need for a different therapeutic approach.