In The Netherlands there is no consensus about criteria for cancelling helicopter emergency medical services (HEMS) dispatches. This study assessed the ability of the primary HEMS dispatch criteria to identify major trauma patients. The predictive power of other early prehospital parameters was evaluated to design a safe triage model for HEMS dispatch cancellations.All trauma-related dispatches of HEMS during a period of 6 months were included. Data concerning prehospital information and inhospital treatment were collected. Patients were divided into two groups (major and minor trauma) according to the following criteria: injury severity score 16 or greater, emergency intervention, intensive care unit admission, or inhospital death. Logistic regression analysis was used to design a prediction model for the early identification of major trauma patients.In total, 420 trauma-related dispatches were evaluated, of which 155 concerned major trauma patients. HEMS was more often cancelled for minor trauma patients than for major trauma patients (57.7% vs 20.6%). Overall, HEMS dispatch criteria had a sensitivity of 87.7% and a specificity of 45.3% for identifying major trauma patients. Significant differences were found for vital sign abnormalities, anatomical components and several parameters of the mechanism of injury. A triage model designed for cancelling HEMS correctly identified major trauma patients (sensitivity 99.4%).The accuracy of the current HEMS dispatch criteria is relatively low, resulting in high cancellation rates and low predictability for major trauma. The new HEMS cancellation triage model identified all major trauma patients with an acceptable overtriage and will probably reduce unjustified HEMS dispatches.