Hyperthermia may accentuate the detrimental consequences of brain injury and worsen the outcome of patients with acute head trauma, especially severe traumatic brain injury (TBI). We explored the effect of different magnitudes and durations of hyperthermia in the first 3 days after injury on the outcome of 7145 patients with acute head trauma, including 1626 with severe TBI. The differences in mortality and unfavorable outcome between the normothermia group, mild fever group, moderate fever group, and high fever group were statistically significant (p<0.001). The mortality and unfavorable outcome of severe TBI patients in the groups also differed significantly (p<0.001). The mortality and unfavorable outcome of patients with 1 day, 2 days, and 3 days of high fever were significantly increased (p<0.01). Our data strongly indicate that both degree and duration of early post-trauma hyperthermia are closely correlated with the outcome of acute TBI patients, especially severely injured ones, which indicates that hyperthermia may play a detrimental role in the delayed mechanisms of damage after acute TBI. Prevention of early hyperthermia after acute head trauma is therefore essential to the management of TBI patients.