Objective:Evaluate the psychometric properties of the Mayo-Portland Adaptability Inventory (MPAI).Design:Rating scale (Rasch) analysis of MPAI and principal component analysis of residuals; the predictive validity of the MPAI measures and raw scores was assessed in a sample from a day rehabilitation program.Setting:Outpatient brain injury rehabilitation.Participants:305 persons with brain injury.Results:A 22-item scale reflecting severity of sequelae of brain injury that contained a mix of indicators of impairment, activity, and participation was identified. Scores and measures for MPAI scales were strongly correlated and their predictive validities were comparable.Conclusions:Impairment, activity, and participation define a single dimension of brain injury sequelae. The MPAI shows promise as a measure of this construct.