We present the case of a 30-year-old female patient with Gilbert's syndrome and gastrointestinal intolerance to proton pump inhibitors (PPI) with longstanding epigastric pain. Laboratory tests were unremarkable, except for a slight elevation of indirect bilirubin due to Gilbert's syndrome. An upper gastrointestinal tract endoscopy showed a diffuse and homogeneous micropolypoid mucosal pattern that involved the entire duodenal bulb. Histopathology analysis revealed gastric heterotopic mucosa with foveolar epithelium and fundic glands. A diagnosis of diffuse duodenal gastric heterotopia was determined. Anti-H2 blockers were prescribed with a significant clinical improvement.