CRASH (Corticosteroid randomisation after significant head injury) is a prospective multi-centre randomised double blind study of methylprednisolone versus placebo in mild, moderate and severe head injury. Patients are eligible up to 8 hours from injury. To date the CRASH trial has recruited 9000 patients. The trial is recruiting from 200 hospitals in 50 countries with another 100 centres planning to join the trial. The target for recruitment is 20,000 patients by 2006. The trial is wholly funded by the Medical Research Council of Great Britain and is multidisciplinary, involving doctors and nurses from a range of specialities. A recent systematic review of corticosteroids in head injury demonstrated a risk of death in the corticosteroid treated group 2% lower than in the control group. The 95% confidence interval ranges from a 60%, lower mortality to a 2% higher mortality. This result is compatible with there being no real benefit, but it is also compatible with there being a small benefit of a few percent. An improvement in mortality of 2% would theoretically save 10,000 lives per 500,000 patients treated. The global impact of such a treatment effect would be significant as the number of head injuries world-wide continues to rise.