Objective: To examine the relationship of premorbid variables, injury severity, and cognitive and functional status to outcome 1 year after traumatic brain injury (TBI) and to assess the feasibility of multivariate path analysis as a way to discover those relationships. Design: Prospective, longitudinal. Settings: Level I trauma center, acute inpatient rehabilitation hospital. Patients: One hundred seven subjects (87 men, 20 women; mean age, 33.91 ± 14.2 yr) who had experienced severe TBI, typically from motor vehicle crashes. Interventions: Acute medical and rehabilitation care. Main Outcome Measures: Disability Rating Scale, Community Integration Questionnaire, and return to employment. Evaluated in acute rehabilitation, and at 6 and 12 months' postinjury. Results: Path analyses revealed that premorbid factors had significant relationships with injury severity, functional skills, cognitive status, and outcome; injury severity affected cognitive and functional skills; and cognitive status influenced outcome. No significant relationships were found between injury severity and emotional status, injury severity and outcome, emotional status and outcome, and functional skills and outcome. Conclusions: Multivariate analysis is important to understanding outcome after TBI. Injury severity, as measured in this study, is less important to 12-month outcome than the premorbid status of the person and the difficulties (particularly cognitive deficits) exhibited at follow-up 6 months after the trauma. © 2001 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.