BACKGROUND: Diagnostic upper gastrointestinal (UGI) endoscopy has been regarded as a safe procedure. CASE REPORT: We report of a 67-year-old woman who developed epigastric pain and dyspeptic complaints following an uneventful upper gastrointestinal endoscopy. The diagnosis of an acute reversible duodenitis was made on the basis of imaging studies. A duodenal diverticulum was also found on CT images, which raised the suspicion that duodenal diverticulum could be a predisposing factor for duodenitis. CONCLUSIONS: Despite significant inflammation the patient demonstrated rapid clinical improvement with conservative treatment. Presence of a duodenal diverticulum may predispose to acute duodenitis following diagnostic UGI endoscopy.