In this exploratory study, we examined the occurrence of duodenogastric bile reflux to the excluded stomach after Roux-en-Y gastric bypass, a standard surgical therapy for morbid obesity. We studied 22 unselected patients (median age 44, 20 females) 18 months postoperatively. BMI at surgery and cholescintigraphy was 45 and 29 kg/m2, respectively. Mebrofenin labeled with 200 MBq 99mT was injected intravenously and the fate of radioactivity followed for 90 min. Bile flow was enhanced with cholecystokinin. We found scintigraphic evidence of duodenogastric bile reflux in 36% of the patients. The tracer remained in the excluded stomach throughout the study period. In conclusion, our investigation indicates that in more than one third of the patients undergoing gastric bypass, the gastric mucosa in the excluded stomach is exposed to the potential deleterious effects of bile.