The basal-bolus concept of delivering insulin to diabetic patients makes physiological sense, as it mimics normal insulin release in people without diabetes. In line with this concept, a major effort put forth by insulin manufacturers has been to develop the ideal exogenous basal insulin product. The perfect basal insulin product would be injected into subcutaneous tissue without causing irritation, release insulin continuously at a constant rate for at least 24 hours, be stable, not contribute to weight gain, have a low risk of allergic reactions and, very importantly, minimize the risk of hypoglycaemia. While the perfect insulin has not yet been discovered, advancements are still being made. Insulin degludec is an ultra-long-acting basal insulin analogue that possesses a flat, stable glucose-lowering effect in patients with type 1 or type 2 diabetes mellitus. Insulin degludec achieves these pharmacokinetic properties by forming soluble multihexamers upon subcutaneous injection, resulting in the formation of a depot in the subcutaneous tissue that is slowly released and absorbed into circulation. Insulin degludec has been associated with slightly less weight gain and fewer nocturnal hypoglycaemic episodes when compared with insulin glargine in some, but not all, clinical studies. This article briefly reviews current evidence for the use of insulin degludec in patients with type 1 or type 2 diabetes mellitus and discusses the potential impact of this new basal insulin on clinical practice.