Objective: To examine age-related differences in rehabilitation outcomes following traumatic brain injury (TBI). Design: Retrospective collaborative study. Setting: Patients received acute neurotrauma and inpatient rehabilitation services at 1 of the 17 National Institute on Disability and Rehabilitation Research-designated Traumatic Brain Injury Model Systems (TBIMS) centers. Participants: A sample of 273 older patients (<55y) admitted for TBI were taken from the TBIMS National Database. Older patients were matched with subjects 44 years of age or younger, based on severity of injury (Glasgow Coma Scale score, length of coma, intracranial pressure elevations). Due to decreasing length of stay (LOS), only patients admitted from 1996 through 2002 were included. Intervention: Inpatient interdisciplinary brain injury rehabilitation. Main Outcome Measures: Acute care LOS, inpatient rehabilitation LOS, admission and discharge FIM instrument and Disability Rating Scale (DRS) scores, FIM and DRS efficiency, acute and rehabilitative charges, and discharge disposition. Results: One-way analyses of variance demonstrated a statistically significant difference between older and younger patients with respect to LOS in rehabilitation but not for acute care. Total rehabilitative charges, and admission and discharge DRS and FIM scores also showed statistically significant differences between groups. Older patients progressed with significantly less efficiency on both the DRS and FIM scales. Significantly more charges were generated per unit for older patients to improve on the DRS scale, but not the FIM scale. Using chi-square analysis, a statistically significant difference in rate of discharge to home was identified between older (80.5%) and younger (94.4%) patients. Conclusions: Results in this study are similar to those in earlier studies with smaller sample sizes. Major differences observed include significantly slower and more costly progress in inpatient rehabilitation for older patients with TBI, as well as a significantly lower rate of discharge to community for older patients. However, even with decreasing LOS in both settings, community discharge rate is still encouraging for older patients with TBI. © 2006 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.