OBJECTIVE: To investigate the concurrent validity and responsiveness of the High-Level Mobility Assessment Tool (HiMAT) in people after traumatic brain injury (TBI). DESIGN: This study compared the concurrent validity and responsiveness of the motor subsection of the FIM instrument and the gross function component of the Rivermead Motor Assessment (RMA) with the HiMAT, a new measure of high-level mobility developed for use in TBI. SETTING: A major rehabilitation hospital. PARTICIPANTS: A convenience sample of 103 participants with TBI were recruited from a major rehabilitation hospital. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: HiMAT, motor FIM, and the gross function RMA. RESULTS: The correlation between the HiMAT and motor FIM was moderate (r=.53, P<.001), largely because of a ceiling effect in the motor FIM. The correlation between the HiMAT and gross function RMA was strong (r=.87, P<.001), yet the gross function RMA was also susceptible to a ceiling effect, with 51.5% of subjects achieving the maximum score. The HiMAT was more responsive than the motor FIM and the gross function RMA on all indices. CONCLUSIONS: The HiMAT is a new unidimensional scale with moderate concurrent validity for measuring high-level mobility. The HiMAT is more responsive and has less of a ceiling effect than either the motor FIM or the gross function RMA.