Background: Insulin degludec is a novel insulin analogue that may reduce the risk of mild nocturnal hypoglycaemia in type 1 diabetes. Patients with type 1 diabetes and recurrent severe hypoglycaemia (high risk patients) are also burdened by nocturnal hyoglycaemia (mild and silent). These episodes may contribute to the developement of hormonal counterregulatory failure and hypoglycaemia unawareness, which in turn increases the risk of further hypoglycaemic episodes, especially epiosdes of severe hypoglycaemia.The effect of insulin degludec on risk of mild nocturnal hypoglycaemia in subjects with type 1 diabetes and high risk of severe hypoglycaemia compared to insulin glargine is to be investigated.