Older adults comprise an increasingly large proportion of patients with traumatic brain injury (TBI) receiving care in inpatient rehabilitation facilities (IRF). However, high rates of comorbidities and evidence of declining preinjury health among older adults who sustain TBI raise questions about their ability to benefit from IRF care. To describe the proportion of older adults with TBI who exhibited minimal detectable change (MDC) and a minimally clinically important difference (MCID) in motor function from IRF admission to discharge; and to identify characteristics associated with clinically meaningful improvement in motor function and better discharge functional status. This retrospective cohort study used Medicare administrative data probabilistically linked to the National Trauma Data Bank to estimate the proportion of patients whose motor function improved during inpatient rehabilitation and identify factors associated with meaningful improvement in motor function and motor function at discharge. Inpatient rehabilitation facilities in the United States. Fee-for-service Medicare beneficiaries with TBI. Minimal Detectable Change (MDC) and Minimally Clinically Important Difference (MCID) in the Functional Independence Measure motor (FIM-M) score from admission to discharge, and FIM-M score at IRF discharge. From IRF admission to discharge 84% of patients achieved the MDC threshold, and 68% of patients achieved the MCID threshold for FIM-M scores. Factors associated with a higher probability of achieving the MCID for FIM-M scores included better admission motor and cognitive function, lower comorbidity burden, and a length of stay longer than 10 days but only among individuals with lower admission motor function. Older age was associated with a lower FIM-M discharge score, but not the probability of achieving the MCID in FIM-M score. Older adults with TBI have the potential to improve their motor function with IRF care. Baseline functional status and comorbidity burden, rather than acute injury severity, should be used to guide care planning.