BACKGROUND Physician-staffed Helicopter Emergency Medical Services (HEMS) provide specialist medical care to the accident scene and aim to improve survival of severely injured patients. Previous studies were often underpowered and showed heterogeneous results, leaving the subject at debate. The aim of this retrospective, adequately powered, observational study was to determine the effect of physician-staffed HEMS assistance on survival of severely injured patients. METHODS All consecutive severely injured trauma patients (ISS >15) between October 1, 2000 and February 28, 2013 were included. Assistance of physician-staffed HEMS was compared with assistance from the ambulance paramedic crew (i.e., EMS group) only. A regression model was constructed for calculating the expected survival and survival benefit. RESULTS A total of 3543 polytraumatised patients with an ISS >15 were treated at the Emergency Department, of whom 2176 patients remained for analysis; 1495 (69%) were treated by EMS only and 681 (31%) patients received additional pre-hospital care of HEMS. The model with the best fit and diagnostic properties (H-L coefficient 2.959, p=0.937; AUC 0.888; PPV 71.4%; NPV 88.0%) calculated that 36 additional patients survived because of HEMS assistance. This resulted in an average of 5.33 additional lives saved per 100 HEMS dispatches for severely injured patients. CONCLUSIONS The present study indicates an additional 5.33 lives saved per 100 dispatches of the physician-staffed HEMS. Given the excellent statistical power of this study (>90%), physician-staffed HEMS is confirmed to be an evidence-based valuable addition to the EMS systems in saving lives of severely injured patients.