Background: Endotracheal intubation (ETI) in patients with traumatic brain injury (TBI) and intact airway reflexes remains controversial. Increased on-scene duration to secure the airway may be a time cost that the patient does not benefit from. We sought to determine the on- scene duration of prehospital intubation performed by anaesthesiologists in patients with moderate and severe TBI, and this information would be helpful in prioritizing when to perform ETI in the prehospital setting.Methods: A retrospective analysis of data was performed concerning patients with head injury and Glasgow Coma Scale (GCS) score <14 during the period of 2006-2010 from a mixed rural/urban Norwegian Helicopter Emergency Medical Services (HEMS). Linear regression was used to determine the additional on-scene duration associated with ETI. Results: Among 183 patients with head injury and GCS score <14, prehospital ETI, high GCS score, and age 16-30 show a significant increase in on-scene duration. Prehospital ETI show the strongest correlation and when adjusted for other variables prove to increase on- scene duration by 13.3 minutes (95% confidence interval [CI]: 8.7-17.9, p<0.001). Conclusion: We estimate that prehospital ETI performed by anaesthesiologists increases on- scene duration for patients with head injury by 13.3 minutes. This knowledge will help anaesthesiologists to determine in which situations prehospital intubation should be performed and thus optimize the treatment of patients with severe head injury.