Congenital hyperinsulinism (HI) of infancy, the most frequent cause of hypoglycaemia in young children, is a neuro-endocrine disease secondary to either focal adenomatous hyperplasia or a diffuse abnormal pancreatic insulin secretion. This inappropriate secretion of insulin induces severe hypoglycaemias that require aggressive treatment to prevent the high risk of irreversible brain damage. Focal and diffuse forms of HI share a similar clinical presentation, but their treatment is dramatically different. Selective surgical resection can cure focal HI whilst diffuse forms require near-total pancreatectomy if resistant to medical treatment. Until recently, preoperative differential diagnosis was based on pancreatic venous sampling, an invasive method, technically difficult to perform, which requires general anaesthesia. The pancreas is one of the most heavily innervated peripheral organs in the body, and its functional imaging with positron emission tomography (PET) is difficult to perform, in part because of the vast number of physiological roles and cell types that characterize this organ. However, HI, as all neuro-endocrine diseases, is notable for the ability to take up amine precursors and to convert them into biogenic amines. Therefore, we have evaluated the use of PET with [18F]fluoro-L-DOPA, a precursor of catecholamines, to image the pancreas and distinguish focal from diffuse HI.