This review encompasses the neurobehavioral sequelae of moderate to severe closed head injury (CHI). Following a discussion of posttraumatic amnesia and its measurement, the paper discusses assessment of the global outcome of CHI using the Glasgow Outcome Scale. Domains of residual neurobehavioral sequelae that are reviewed include attention/information processing speed, memory, language, intellectual ability, executive functions, and motor speed. The contribution of behavioral disturbance and psychosocial maladjustment to overall outcome is reviewed, as is the impact on the family. Finally, the neurobehavioral outcome measures for clinical trials involving moderate to severe head-injured patients are presented. Caveats for completing clinical trials that involve assessment of neurobehavioral functioning are provided.