Hypoglycaemia is a common cause of presentation to the emergency department (ED) for people with diabetes mellitus. Patients experiencing a hypoglycaemic episode require prompt treatment with fast-acting glucose to prevent brain fuel deprivation and functional brain failure, therefore it is vital that ED nurses can recognise the signs and symptoms of hypoglycaemia and are aware of the factors that can compound or mask it. This article discusses the aetiology and signs and symptoms of hypoglycaemia in adults with type 1 and type 2 diabetes and describes the use of an algorithm for the management of hypoglycaemia in this patient population in hospital. The author also discusses how ED nurses can try to identify the cause of the hypoglycaemic episode and work with patients, their relatives or carers and the wider multidisciplinary team to prevent reoccurrence.