Objective: To validate a model that examines the contribution of premorbid variables, injury severity, and functional and cognitive status to outcome 1 year after traumatic brain injury (TBI). Design: Cross-validation study using a larger, national, prospective, longitudinal sample. Setting: Acute inpatient rehabilitation hospitals at Traumatic Brain Injury Model Systems centers. Participants: Two sample populations followed through acute rehabilitation to 1 year after TBI. The original sample included 107 patients, and the cross-validation sample included 294 patients. Participants were predominately young men who had experienced moderate to severe TBI in motor vehicle crashes. Interventions: Acute medical and rehabilitation care. Main Outcome Measures: Disability Rating Scale, Community Integration Questionnaire, and return to employment. Results: Structural equation modeling was used to compare the fit of the data to a path analysis developed through clinical use and previous research. Both samples provided adequate goodness of fit, supporting the model's validity. Injury severity affected cognitive and functional status, and cognitive and functional status significantly influenced 1-year outcome. Premorbid factors and injury severity did not directly influence outcome. Conclusions: Both samples supported the proposed model, which was cross-validated. Injury severity indirectly influences outcome through its effects on cognitive and functional status. Although treatment to decrease injury severity is obviously important, concentrated rehabilitation interventions aimed at improving patients' cognitive and functional status may have a more significant impact on 1-year outcome and should be the focus of future research.