Persistent hyperinsulinemic hypoglycaemia is caused most commonly by an insulinoma in adults or by nesidioblastosis in neonates. In adults, localised islet cell hyperplasia is a rare disorder characterised by localised proliferation of islet cells. The authors present the case of a previously healthy non-obese middle aged female with new-onset severe hypoglycaemia. Laboratory findings confirmed a case of hyperinsulinemic hypoglycaemia. Endoscopic ultrasonography, intra-arterial calcium stimulation test and intraoperative ultrasonography showed a lesion in the uncinate process that was enucleated. Rest of the pancreas was normal. Histological examination and immunostaining of the resected tissue revealed pancreatic tissue with maintained acinar pattern consistent with diagnosis of localised islet cell hyperplasia. The patient did not have further episodes of hypoglycaemia following the procedure. Localised islet cell hyperplasia with such a very high insulin level is exceedingly rare in adult populations and not reported in literature. This diagnosis cannot be easily made through routine diagnostic laboratory or radiological procedures and likely requires a histological diagnosis. Management of this rare entity is by enucleation.