Insulin detemir (Levemir) is a soluble long-acting human insulin analogue acylated with a 14-carbon fatty acid. The fatty acid modification allows insulin detemir to reversibly bind to albumin, thereby providing slow absorption and a prolonged and consistent metabolic effect of up to 24 hours in patients with type 1 or type 2 diabetes mellitus. Insulin detemir has a more predictable, protracted and consistent effect on blood glucose than neutral protamine Hagedorn (NPH) insulin, with less intrapatient variability in glycaemic control, compared with NPH insulin or insulin glargine. Insulin detemir, administered once or twice daily, is at least as effective as NPH insulin in maintaining overall glycaemic control, with a similar or lower risk of hypoglycaemia, especially nocturnal hypoglycaemia, compared with NPH insulin in patients with type 1 or type 2 diabetes. Insulin detemir also provides the added clinical benefit of no appreciable bodyweight gain in patients with type 1 diabetes and less bodyweight gain than NPH insulin in patients with type 2 diabetes. Insulin detemir is, therefore, a promising new option for basal insulin therapy in patients with type 1 or 2 diabetes.