PURPOSE: To assess the prognostic value of admission perfusion computed tomography (CT) in patients with severe head trauma. MATERIALS AND METHODS: This prospective study included 130 patients with severe trauma, aged 19-86 years, admitted with a Glasgow Coma Scale score of 8 or less. They underwent perfusion CT as part of their admission CT survey. Clinical data, unenhanced cerebral CT findings, and perfusion CT scans were evaluated with respect to the Glasgow Outcome Scale (GOS) score at 3 months. Perfusion CT features were evaluated in patients with intracranial hypertension, cerebral contusions, and juxtadural hematomas. Ordered logistic regression was used to determine risk factors for an unfavorable GOS score at 3 months. RESULTS: Perfusion CT was more sensitive than conventional unenhanced CT in the detection of cerebral contusions. Perfusion CT featured specific patterns with respect to patient outcome, with normal brain perfusion or hyperemia in patients with favorable outcome, and oligemia in patients with unfavorable outcome. The number of arterial territories with low regional cerebral blood volume at perfusion CT was an independent prognostic factor (P =.008), as were mean arterial pressure at the scene of accident (P =.083), base excess at admission (P =.002), presence of skull fractures (P =.041), and signs of herniation (P =.013) at admission unenhanced cerebral CT. Perfusion CT also showed a range of brain perfusion alterations in patients with juxtadural collections, cerebral edema, or intracranial hypertension. CONCLUSION: Perfusion CT in patients with severe head trauma provides independent prognostic information regarding functional outcome.