The global epidemic of head injuries is just beginning. Many are caused by road traffic crashes. It is estimated that, by 2020, road traffic crashes will have moved from its present position of ninth to third in the world disease burden ranking, as measured in disability adjusted life years. In developing countries, it will have moved to second. The Corticosteroid Randomisation After Significant Head Injury (CRASH) trial is a large-scale, randomised, controlled trial, among adults with head injury and impaired consciousness, of the effects of a short-term infusion of corticosteroids on death and on neurological disability. Following a successful pilot phase, which included over 1000 randomised participants, the main phase of the trial is now underway. Over the next 5 years, the trial aims to recruit a total of 20,000 patients. Such large numbers will only be possible if hundreds of doctors and nurses can collaborate in emergency departments all over the world. The trial is currently recruiting, and new collaborators are welcome to join the trial (see ).