Severe mechanical trauma to the brain is associated with a high rate of morbidity and mortality. Vigorous treatment must be started immediately if the patient's prognosis is to be improved. Recently, Rosomoff and co-workers1revived interest in hypothermia as a therapeutic tool by their experimental observations on animals. Lazorthes and Campan,2in France, were able to reduce mortality rates in human patients by artificial hibernation, and this technique has become an acceptable adjunct to the treatment of brain injury.3 In 1961, one of us (W.F.B.) began to treat every patient having severe brain injury with immediate hypothermia. Surface cooling was started in the emergency room to reduce the rectal temperature to 87.8 F (31 C) within 90 minutes. Of 14 consecutive patients, ten harbored subdural hematomas. This was a much higher incidence than reported in a larger series4not treated with hypothermia. In addition, hyperthermia was