Severe injury activates multiple chemical pathways causing inflammation and harming vital organs, which can lead to long-term disability and death. The kidney hormone erythropoietin controls red blood cell production and is a common treatment for anemia, but it also reduces inflammation. Previous studies suggest erythropoietin may reduce death and serious disability after severe injury, without an increase in side effects. We will perform a study involving 2500 adults with severe injuries in five countries (New Zealand, Australia, Republic of Ireland, United Kingdom and Finland) who will receive either erythropoietin or a dummy injection under the skin, in addition to all usual treatment. Participants will be assessed after six months to determine their survival and level of disability. If this simple treatment can reduce death and disability after severe injury, it would have worldwide practice-changing effects.