We propose to do a pilot study of 50 children admitted with severe TBI to paediatric intensive care units in Australia and New Zealand. Severe TBI will be defined as children with either (i) Glasgow Coma Scale (GCS) ≤ 8 and an abnormal CT scan or (ii) motor score of ≤ 3 and normal CT scan. Children will be included only if they can be randomised within 6 hours of the injury occurring. Patients will be stratified a priori by (i) centre and (ii) Glasgow Coma Score. One half will be cooled to 32-33°C for 72 hours and then slowly rewarmed. If intracranial hypertension occurs during or after rewarming, the hypothermia group will have cooling continued until intracranial pressure (ICP) is controlled. The other half will have their temperature maintained at 36-37°C. All other aspects of care will be managed with a standardised protocol.