Over the past 10 years, rehabilitation has assumed a primary role in the care and treatment of the patient with severe traumatic brain injury (TBI). This has brought about increased attention to factors influencing outcome in this population. This article discusses the “state of the art” in assessment, treatment, and research specific to the underresponslve patient with severe TBI. Issues concerning diagnostic accuracy, methods of assessment, prognostic indicators, and treatment interventions are considered in relation to outcome. Recommendations for advancing the state of the art during the next decade are offered