Congenital hyperinsulinusm is rare disease characterized high secretion of insulin by pancreatic beta cells leading to the development of hypoglycemia. Persistent and transient forms of hyperinsulinism are distinguished. Transient hyperinsulinism are the most common cause of severe hypoglycemia in newborns. The etiology of this disease is not known. There are risk factors for the development of transient hyperinsulinism: asphyxia at birth, prematurity, maternal diabetes, low or large weight by gestation. Hypoglycemia with hyperinsulinism is severe. Therefore, early diagnosis and therapy especially during the neonatal period, are necessary.The article describes 3 clinical cases of transient hyperinsulinism in children with different gestational age and concomitant pathology. All children recevied insulinostatic therapy with diazoxide with a positive effect: euglycemia without glucose requirement . In all children, therapy was completed subsequently. At the time of publication of the article, the physical and psychomotor development of children is normal.