A group of 1,273 blunt trauma patients who were treated and transported from the site of injury by seven different hospital-based rotorcraft aeromedical emergency care services were studied using a methodology based on injury severity designed to predict the mortality of such patients. The methodology predicted that 241 patients should have died; 191 patients did die. This 21% reduction in expected mortality was highly significant (P less than .001). Each of the seven rotorcraft services had a reduction in predicted mortality. The reduction was statistically significant (P less than .05) in five of the seven aeromedical services, or 86% of the total patient cohort. Hospital-based rotorcraft aeromedical emergency care services may reduce the expected mortality of blunt trauma patients treated at the site of injury.