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Background: Because management is very different, it is important to differentiate between small focal insulinomas and diffuse pancreatic dysplasia (nesidioblastosis) in patients with confirmed endogenous hyperinsulinaemic hypoglycaemia (EHH). Most insulinomas highly express glucagon-like peptide-1 receptors enabling positron emission tomography-computed tomography imaging with its radiolabelled analogue; 68 Ga-DOTA-Exendin-4 (Exendin)., Aim: To determine: (i) the utility of Exendin in EHH patients in a clinical setting; and (ii) whether the degree of Exendin uptake differentiates non-insulinoma pancreatogenous hypoglycaemia syndrome (NIPHS) from post-gastric bypass hypoglycaemia (PGBH)., Methods: This retrospective study reviewed the clinical, biochemistry and prior imaging findings in confirmed EHH patients referred for Exendin. Accuracy of Exendin was based on surgical findings and treatment outcomes. Finally, average Exendin uptake (SUVmax) of five PGBH studies was compared with the SUVmax of a key NIPHS case report., Results: Twenty of 25 consecutive patients had confirmed EHH. Exendin located insulinomas in eight of nine patients enabling successful surgical excision with rapid and durable cure. Exendin correctly identified diffuse nesidioblastosis in two of three cases requiring partial pancreatectomy for hypoglycaemia control. All three relapsed within 1.7 years with one needing completion pancreatectomy. Establishing the cause in the remainder relied on other investigations, clinical correlation and response to empirical treatment. Finally, Exendin SUVmax could not distinguish between NIPHS and PGBH., Conclusion: In EHH patients, Exendin accurately identifies the site of insulinoma and thereby differentiates it from nesidioblastosis but negative findings should not be ignored. Exendin is unlikely to differentiate between normal pancreatic uptake, NIPHS and PGBH., (© 2020 Royal Australasian College of Physicians.)