The medical treatment is based on proglycem, or diazoxide, then octreotide (Sandostatine ®, Novartis) with a dose of 10 to 50 µg/Kg/jour divided to three subcutaneous injections. Most neonates are resistant to diazoxide and side effects are observed (important edema and hypertrichosis). The Sandostatine® is a much more effective treatment, unfortunately with a short half-life and painful injections. In the cases of resistance to the medical treatment, the distinction of the two forms is essential to guide the surgical treatment : partial pancreatectomy in the focal forms, curing definitively hypoglycemia; subtotal pancreatectomy in the diffuse forms resisting to the medical treatment, leading to a diabetes and a pancreatic exocrine insufficiency. Also, the medical treatment is essential in the case of the diffuse forms to avoid a subtotal pancreatectomy. Mutations in two genes encoding the potassium channels, SUR1 and KIR6.2, are responsible for hyperinsulinism resistant to diazoxide.