The Boston Emergency Medical Service system was studied to determine the effects of Advanced Life Support (ALS) prehospital trauma care compared to Basic Life Support (BLS) treatment. The severity of injury and clinical status of patients was defined and monitored using the Trauma Score (TS) described by Champion. The TS on arrival at the hospital increased significantly more for patients receiving field ALS care than for patients transported by BLS ambulances (p = 0.01). ALS resuscitation had most influence on patients with TS 4-13 and did not delay transport time. Furthermore, a positive change in prehospital TS was significantly related to an increased chance of long-term survival for any given severity of injury (p = 0.0002). From these data we conclude that the TS is useful for prehospital triage and that appropriate field ALS resuscitation results in more favorable outcomes following major trauma.