Fever above 38C that occurs in patients with acute neurosurgical diseases appears to worsen secondary brain injury and ultimate neurologic outcomes. Laboratory investigations are quite clear regarding the adverse effects of fever in terms not only of functional outcomes, but also histologic and neurochemical injury. Several preliminary clinical studies also suggest worsened neurologic outcomes in patients who are febrile compared to those who are not. Unfortunately, however, a large prospective study of 428 patients with acute neurosurgical diseases has shown that fever is extraordinarily common during the first seven days after subarachnoid hemorrhage, stroke, and TBI. The ability to eliminate fever in most of these patients during the first five to seven days after their injury would seem desirable. Based on a phase-I trial, it appears that intravascular cooling is a promising new method for avoiding fever in the neurosurgical ICU.