Neonatal hyperglycaemia may be permanent or, more often, transient. Transient hyperglycaemia occurs mainly in premature and low-birth-weight neonates, especially if they are stressed or receive endovenous glucose. There is no clinical or biological sign allowing to predict these children future at the time of diagnosis, even if the seriousness of hyperglycemia, the collapse of insulin secretion, and the association to complex pathologies is more usual in permanent diabetes. This explains why the treatment must be the same, namely precocious insulin therapy.