The most common cause of persistent hypoglycaemia in infancy represents congenital hyperinsulinism. In their review Marquard and colleagues point out that this is biochemically characterized by an upregulated secretion of insulin from pancreatic beta cells in relation to blood glucose concentration. Up to now, eight different genes are described in relation to this disease. Nevertheless, in still up 50% of patients the genetic basis remains unkown. The clinical presentation is heterogenous with regard to age of onset, severity and symptoms. During the last years, substantial progress has been made, mainly by 18F-L- dopa differentiating diffuse and focal disease. Treatment in diffuse forms includes mainly attempts with diazoxide and octreotide. In patients with the focal form a limited pancreatectomy can lead to the cure of