Congenital hyperinsulinism is a rare disorder that commonly presents in the immediate postnatal period as persistent hypoglycemia. The condition is frequently resistant to medical therapies, and the genetic mutations implicated in the disorder can be predictive of response to therapy. Evaluation of hypoglycemia in the illustrative case presented in this article led to genetic testing identifying recessive mutations in the potassium channel subunits of the beta-islet pancreatic cells. Potassium channel defects are often refractory to medical therapies, so near-total pancreatectomy is usually indicated; however, genetic mutations leading to metabolic dysregulation within the beta-islet pancreatic cells are usually responsive to medical therapy. Aggressive treatment of hypoglycemia in the setting of congenital hyperinsulinism is important to prevent long-term neurologic sequelae secondary to hypoglycemia-induced brain injury.