The primary aim of the outcome study will be to determine whether, in children with severe TBI, prolonged initial hypothermia improves the proportion with good outcome 12 months after injury when compared to initial normothermia. Outcome will be assessed at 6 and 12 months. The primary outcome measure will be a Paediatric Cerebral Performance Category (PCPC) at 12 months after the date of injury, dichotomized to poor outcome (categories 4-6) and good outcome (categories 1-3). Secondary outcome measures will be (i) PCPC at 6 after injury (ii) standardised tests (intelligence and memory, functional outcome, attention, executive functions) 12 months after injury (iii) ICP and cerebral perfusion pressure (CPP) during the first 5 days of treatment (v) frequency and nature of interventions to control ICP/CPP (vi) duration of mechanical ventilation and (vii) potential adverse events.