A 51-year-old woman complaining of weakness in the limbs was diagnosed as having a duodenal gastrinoma on performing a further evaluation. Surgical resection was performed with selective arterial calcium injection for localization. During preoperative hospitalization, she experienced recurrent severe vomiting and diarrhea after endoscopy, leading to acute kidney injury. To our knowledge, this is the first report of gastrinoma with post-endoscopy symptom exacerbation. Although the etiology is unknown, the findings in this case suggest that sufficient fluid replacement, sedation, and high-dose proton pump inhibitor administration should be taken into consideration when performing endoscopy in gastrinoma patients.