The use of helicopter emergency medical services (HEMS) for the transportation and treatment of trauma patients, while commonplace in most developed nations, remains controversial. The purported beneficial effects of HEMS compared to ground emergency medical services is likely to be some combination of speed, crew expertise, and the fact that HEMS is part of an organized trauma system. When the HEMS literature is assessed as a whole, considerable heterogeneity of effects and study methodologies preclude an accurate estimate of composite effect. However, when the outcome of mortality is studied using advanced multivariable regression techniques to control for multiple known confounders, an improved odds of survival has been repeatedly demonstrated. Future HEMS research must rely on robust observational study designs and assessments of a variety of patient outcomes. Questions about the role of speed, distance, and other potentially beneficial elements of HEMS remain.