The differences between brain and bladder temperature (delta T), and the relationship of delta T to cerebral perfusion pressure (CPP) and jugular venous oxygen saturation (SjO₂) were studied during hypothermia in 11 patients with severe traumatic brain injury, of whom 5 underwent conservative treatment for diffuse axonal injury (DAI) (DAI group) and 6 who underwent decompressive craniectomy for hematoma (SDH group). All patients underwent hypothermia treatment. Brain temperature was monitored via an intraparenchymal catheter. Bladder temperature was used as the core temperature. SjO₂ was measured continuously. The outcome of all patients was evaluated at discharge using the Glasgow Outcome Scale. Delta T in the SDH group was significantly lower than that in the DAI group. No relationship was found between delta T and CPP during the investigation period. A significant correlation between delta T and SjO₂ was seen in the DAI group, but not in the SDH group. Decompressive craniectomy affects the brain temperature through external environmental factors. Measurement of brain temperature may be a reliable indicator of cerebral blood flow and brain metabolism in patients with DAI and closed cranium during hypothermia. Further experience is required to test this proposal.