Patients in emergency situations with impaired consciousness are unable to give informed consent to participate in clinical trials. In this situation, some ethics committees ask that consent is obtained from a relative or a legal representative. Others however, waive the need for informed consent and allow the doctor in charge to take responsibility for entering such patients. This study used data from the MRC CRASH Trial, an international randomised controlled trial of corticosteroids in head injury, to assess whether the practice of waiving consent results in earlier administration of the trial treatment. It was found that time from injury to randomisation was significantly reduced (1.2 hours, 95% CI 0.7 to 1.8 hours) and patient recruitment was higher in hospitals where consent was waived compared with those that required relatives consent.