Insulinoma is a neuroendocrine tumour of islet cells and a rare cause of hypoglycaemia in both adults and the paediatric population, with an incidence is 1–4 cases/million/year. Insulinoma may occur as an isolated tumour or as a component of multiple endocrine neoplasia syndrome 1. In the case presented below, a 15-year-old female patient with no significant medical history was brought to the emergency department by a medical rescue team, exhibiting symptoms of neuroglycopaenia for several hours. After excluding more common causes of hypoglycaemia, insulinoma was suspected. Given the patient’s very young age at onset and a significant family history, laboratory and imaging diagnostics were performed for multiple endocrine neoplasia syndrome 1. Once more common causes have been ruled out, insulinoma should be considered in the differential diagnosis of hypoglycaemia. If the diagnosis of insulinoma is confirmed, the possibility of multiple endocrine neoplasia syndrome 1 should be considered.