The records of 916 trauma victims transported by an emergency helicopter service were reviewed to evaluate its impact on patient outcome. According to strict criteria, the service was classified as essential, helpful, or "not a factor" in the preservation of life and/or limb in each case. The helicopter service was essential in 14.0%, helpful in 12.9%, and "not a factor" in 56.6% of patients. A fourth category included patients who, despite the delivery of maximal emergency medical care, died as a result of their injuries (16.5%). With the available initial information, it was impossible to determine prospectively which patients would benefit from air transport. We believe that the rapid evaluation of potentially serious injuries and the number of patients for whom the service proved beneficial justify its use, particularly in rural areas.