Diabetic ketoacidosis (DKA) is an acute and serious metabolic complication of type 1 diabetes. Caused by severe insulin deficiency leading to hyperglycaemia, DKA is the most common cause of mortality in people with type 1 diabetes under the age of 40. It causes nausea and vomiting, hypothermia, hypotension, cardiac arrhythmia, tachycardia, deep and rapid breathing and, if untreated, can lead to cerebral oedema, coma and death. The survival of patients with DKA can depend, therefore, on the ability of emergency nurses to recognise its signs and symptoms. The most urgent treatment outcomes in emergency settings are the reversal of ketosis and hyperglycaemia, and the prevention of hypokalaemia and hyponatraemia, and these should be followed by hourly biochemical tests to determine treatment alterations. This article describes DKA and how patients with the condition usually present, and outlines its treatment by emergency nurses.