Recently the Paediatric Association of the Netherlands (NVK) published a new guideline on the treatment of diabetic ketoacidosis (DKA) and hyperglycaemic hyperosmolar syndrome (HHS) in children and adolescents. DKA comprises hyperglycaemia, ketosis and acidosis. Cerebral oedema is a feared, life-threatening complication of DKA. HHS is characterized by hyperglycaemia, hyperosmolarity, severe dehydration, and little or no ketone production. Multi-organ failure, rhabdomyolysis and thrombosis are the most common complications. The NVK guideline distinguishes between treatment of DKA and treatment of HHS, in contrast with the draft version of the Netherlands Association of Internal Medicine guideline on diabetes. To prevent cerebral oedema in children with DKA, it is necessary that both rehydration and metabolic correction are done slowly and carefully. Use of hypotonic fluids is not recommended. Correction of hyperglycaemia is of secondary importance and insulin should be started at a low dosage. Correction of intravascular hypovolaemia is the most important treatment in children with HHS. If adequate fluid replacement does not cause serum glucose levels to drop sufficiently, then administration of insulin should be considered. Fluid replacement is the initial treatment of HHS. Insulin administration should be considered when serum glucose concentrations are no longer declining adequately with fluid administration alone.