BACKGROUND: Morbid obesity is associated with gastroesophageal reflux (GERD). The aim of this prospective study was to determine esophageal motility in asymptomatic morbidly obese patients and compare it to non-obese individuals. METHODS: Forty-seven morbidly obese patients without GERD symptoms and 15 normal weight individuals were divided into four groups according to their body mass index (BMI; group I, <30 kg/m; group II, 35-39.9 kg/m; group III, 40-49.9 kg/m; group IV, ≥50 kg/m). Standard stationary water-perfused manometry was performed for the assessment of anatomy and function of the lower esophageal sphincter (LES). Twenty-four-hour ambulatory pH-metry and measurement of esophageal motility were performed with a microtransducer sleeve catheter. Data are given as mean ± SD, and the results of groups II-IV were compared to the non-obese individuals from group I. RESULTS: Patients with morbid obesity had significantly lower LES pressures than non-obese individuals (I, 15.1 ± 4.9; II-IV, 10.5 ± 5.4, mmHg, p < 0.05 vs. I) and showed an altered esophageal motility with respect to contraction frequency (I, 1.8 ± 0.7/min; II-IV, 3.6 ± 2.5/min; p < 0.05 vs. I) and contraction amplitude (I, 38 ± 12 mmHg; II-IV, 33 ± 17 mmHg; p < 0.05 vs. I). Furthermore, these patients had significantly higher DeMeester scores than non-obese individuals. Length and relaxation of the LES as well as propulsion velocity of the tubular esophagus did not differ. CONCLUSION: Patients with morbid obesity (=BMI > 40 kg/m) have a dysfunction of the LES and an altered esophageal motility, even when they are asymptomatic for GERD symptoms.