Congenital hyperinsulinism (CHI or HI) is a condition leading to recurrent hypoglycemia due to an inappropriate insulin secretion by the pancreatic islet beta cells. HI has two main characteristics: a high glucose requirement to correct hypoglycemia and a responsiveness of hypoglycemia to exogenous glucagon. HI is usually isolated but may be rarely part of a genetic syndrome (e.g. Beckwith-Wiedemann syndrome, Sotos syndrome etc.). The severity of HI is evaluated by the glucose administration rate required to maintain normal glycemia and the responsiveness to medical treatment. Neonatal onset HI is usually severe while late onset and syndromic HI are generally responsive to a medical treatment. Glycemia must be maintained within normal ranges to avoid brain damages, initially with glucose administration and glucagon infusion then, once the diagnosis is set, with specific HI treatment. Oral diazoxide is a first line treatment. In case of unresponsiveness to this treatment, somatostatin analogues and calcium antagonists may be added, and further investigations are required for the putative histological diagnosis: pancreatic (18)F-fluoro-L-DOPA PET-CT and molecular analysis. Indeed, focal forms consist of a focal adenomatous hyperplasia of islet cells, and will be cured after a partial pancreatectomy. Diffuse HI involves all the pancreatic beta cells of the whole pancreas. Diffuse HI resistant to medical treatment (octreotide, diazoxide, calcium antagonists and continuous feeding) may require subtotal pancreatectomy which post-operative outcome is unpredictable. The genetics of focal islet-cells hyperplasia associates a paternally inherited mutation of the ABCC8 or the KCNJ11 genes, with a loss of the maternal allele specifically in the hyperplasic islet cells. The genetics of diffuse isolated HI is heterogeneous and may be recessively inherited (ABCC8 and KCNJ11) or dominantly inherited (ABCC8, KCNJ11, GCK, GLUD1, SLC16A1, HNF4A and HADH). Syndromic HI are always diffuse form and the genetics depend on the syndrome. Except for HI due to potassium channel defect (ABCC8 and KCNJ11), most of these HI are sensitive to diazoxide. The main points sum up the management of HI: i) prevention of brain damages by normalizing glycemia and ii) screening for focal HI as they may be definitively cured after a limited pancreatectomy.