Current algorithms for assessment of the severity of brain injury include Glasgow Coma Scale score and other measures. These measures are adequate for relating acute severity but are insufficiently sensitive for subtle pathology which can result in persistent deficit. The Glasgow Coma Scale (GCS) and other measures also do not enable differentiation among types of injury. Thus patients grouped into a single GCS level entering a clinical trial may have vastly heterogeneous severity and type of injury. Because outcomes also vary accordingly, inappropriate classification undermines the integrity of a clinical trial. Improved classification of injury will enable more precise delineation of disease severity and type for patients with a traumatic brain injury (TBI) in clinical trials.