A study of 150 comatose patients transferred to one neurosurgical unit after head injury showed that untoward incidents which could cause secondary brain damage were present in 61 patients, and that extracranial injuries were overlooked or inadequately treated in 21. The commonest mishaps were airways obstruction and hypotension, which affected outcome adversely. Distance from the neurosurgical unit had little effect on rapidity of transfer or the occurrence of untoward incidents. Optimum care requires the rapid transfer of many comatose patients to neurosurgical units, and a systematic approach to minimising the hazards of transfer would reduce mortality and morbidity.