Traumatic injury is a major public health problem with an immense societal cost. Despite improvements in trauma management, patients continue to suffer significant morbidity and mortality. Evidence suggests that males and females tolerate severe injury differently with a greater protection afforded to females. Determining the mechanisms responsible for these sex-based outcome differences after injury, focusing specifically on the early sex-hormone environment post-injury, may allow those at highest risk for poor outcome to be predicted and promote interventions that can improve outcomes for all injured patients. The goal of this study is to determine if the early sex hormone environment soon after injury has effects on the intensity of the immune response, resuscitation and blood transfusion requirements, and important clinical outcomes including mortality, organ failure and infection, following significant injury.