Diabetic ketoacidosis may be associated with a wide variety of complications, some of which are uncommon and not widely appreciated. A case of severe ketoacidosis with multiple complications including septicaemia, pneumomediastinum, gastro-intestinal haemorrhage, magnesium depletion and multiple mononeuropathy is reported in a 17-year old girl who made a successful recovery. The patient had not taken insulin for almost 4 days, had no preceding illness and was admitted in a near moribund state with hypothermia (34.2 degrees C), hypotension (80/50) and an arterial pH less than 6.8. There was a leukocytosis 41,200, the blood culture grew haemolytic streptococci and chest radiology showed pneumomediastinum. I.v. therapy was continued for some days and the patient developed clinical features of magnesium depletion. During the recovery period she developed multiple mononeuropathy. A brief review of these complications is given.