Congenital hyperinsulinism of infancy is the commonest cause of persistent and recurrent hypoglycaemia in the neonatal and infancy period. It is a heterogeneous disorder with respect to clinical presentation, histology, molecular biology and genetics. The biochemical profile is one of hypoketotic, hypofattyacidemic hypoglycemia. To prevent permanent brain damage from hypoglycemia, the treatment of infants with congenital hyperinsulinism must be prompt and aggressive. The drugs used in the medical therapy for congenital hyperinsulinism are diazoxide, octreotide, glucagon and nifedipine.