Gastrinoma is a gastrin-secreting pancreatic neuroendocrine syndrome that presents with a constellation of symptoms referred to as Zollinger–Ellison syndrome (ZES). Patients often present with refractory peptic ulcer disease and diarrhea. Due to the indolent course, time from symptom onset to diagnosis may be delayed. Initial screening is performed with elevated fasting gastrin levels and gastric acid secretion followed by secretin stimulation test for confirmation. Approximately 25% of ZES cases are associated with multiple endocrine neoplasia type 1 (MEN-1), therefore patients with a suspected gastrinoma should also be screened for MEN-1. Gastrinomas are primarily treated with surgical resection but also necessitate long-term acid suppression and management of MEN-1 when applicable. Locally invasive or metastatic disease with unresectable tumors require multidisciplinary approach for chemotherapy, radiofrequency ablation, and chemo/radioembolization.