Objective: To investigate the therapeutic effect of mild hypothermia on severe traumatic brain injury.Methods: Eighty-six in-patients with severe traumatic brain injury treated ordinarily were consecutively randomized into two groups: a hypothermia group (n=43) and a normothermia group (the control group, n=43). In the hypothermia group, the core temperature (i.e., nasopharyngeal or brain temperature) of the patient was reduced to and maintained at 33-35℃ with a systemic cooling blanket. Natural rewarming began after 3-5 days (mean: 4.3 days) of hypothermia treatment. In the control group, the patient received no hypothermia treatment. The vital sign, extradural pressure and serum superoxide dismutase were observed and measured during treatment, and the complications as well as the Glasgow outcome scale were evaluated at 2 years after injury.Results: The mean extradural pressure in the hypothermia group (27.38 mm Hg±4.88 mm Hg at 24 hours, 29.40 mm Hg±4.50 mm Hg at 48 hours and 26.40 mm Hg±4.13 mm Hg at 72 hours after injury) was much lower than that in the control group (32.63 mm Hg±3.00 mm Hg, 34.80 mm Hg±6.00 mm Hg and 31.81 mm Hg±4.50 mm Hg respectively at 24, 48 and 72 hours, P