BACKGROUND The most widely used and most studied coma score to date is the Glasgow Coma Scale (GCS), which is used worldwide to assess level of consciousness and predict outcome after traumatic brain injury (TBI). Our aim was to determine whether the Full Outline of UnResponsiveness (FOUR) score is an accurate predictor of outcome in TBI patients and to compare its performance to GCS. METHODS We prospectively identified TBI patients admitted to our Neuro-ICU between July 2010 and February 2011. We enrolled 51 patients. The FOUR score and GCS were determined by one of the investigators. Outcomes were in-hospital mortality, and poor neurologic outcome (Glasgow Outcome Scale (GOS) 1-3 and Modified Rankin Scale (mRS) score 3-6) at 3-6 months. RESULTS There was a high degree of internal consistency for both the FOUR score (Cronbach's alpha = 0.89) and GCS (Cronbach's alpha = 0.85). In terms of predictive power for in-hospital mortality, the area under the receiver operating characteristic (ROC) curve was 0.93 for FOUR score and 0.89 for GCS. In terms of predictive power of poor neurologic outcome at 3-6 months, the area under the ROC curve was 0.85 for FOUR score and 0.83 for GCS as evidenced by GOS 1-3, and 0.80 for FOUR score and 0.78 for GCS as evidenced by mRS 3-6. The odds ratio (OR) for in-hospital mortality was 0.64 (0.46-0.88) from FOUR score and 0.63 (0.45-0.89) from GCS, for poor neurologic outcome was 0.67 (0.53-0.85) from FOUR score and 0.65 (0.51-0.83) from GCS for GOS, and was 0.71 (0.57-0.87) from FOUR score and 0.71 (0.57-0.87) from GCS for mRS. CONCLUSIONS The FOUR score is an accurate predictor of outcome in TBI patients. It has some advantages over GCS, such as all components of FOUR score but not GCS can be rated in intubated patients.