Objective. Prevention of secondary insults, such as hyperthermia, is a major goal after traumatic brain injury. The aim of our study was to identify risk factors for early hyperthermia in severe head-injured patients. Design. Retrospective cohort study. Setting. A 17-bed multidisciplinary ICU of a 700-bed teaching hospital. Patients. A total of 101 adult patients admitted from January 1999 to December 2001 requiring continuous monitoring of intracranial pressure according to international guidelines. Measurement and results. Forty-four patients experienced early hyperthermia (at least one episode of body temperature 38.5C within the first 2days). On univariate analysis five variables were associated with early hyperthermia: sex; body temperature; white blood cell count on admission; prophylactic use of acetaminophen; and diabetes insipidus within 2days. On multivariate analysis, white blood cell count 14.5109/l on admission (odds ratio, 7.1; 95% confidence interval, 2.420.5; p=0.001) and a body temperature on admission 36C (odds ratio, 6.7; 95% confidence interval, 2.3-20.1) were strong risk factors of early hyperthermia. Prophylactic use of acetaminophen was negatively associated with early hyperthermia (odds ratio, 0.1; 95% confidence interval, 0.020.4). Patients who experienced early hyperthermia were less prone to have good recovery (GOS=5; p=0.03). More patients with severe or moderate disability (GOS=3 or 4) experienced early hyperthermia (p=0.01). Conclusion. We identified a subgroup of patients at high risk of early hyperthermia, which is common in severe head-injured patients. These results could have clinical implications for prevention of hyperthermia after traumatic brain injury in adults.