Acute traumatic brain injury (TBI) in older veterans is an under-recognized public health emergency for the Veterans Health Administration (VHA). The fastest rising incidence of TBI in the United States is in older adults, who have higher mortality, lower rates of functional recovery, and higher risk for post-TBI dementia. Pre-existing TBI, medical/psychiatric conditions, and substance use-common in older veterans-are emerging risk factors for TBI and worse outcomes thereafter. There is an urgent need to characterize acute TBI in older veterans to inform effective interventions to optimize outcomes. We aim to characterize military, clinical, and biological features using a combination of TBI common data elements (CDEs) and validated dementia and geriatrics research assessments. This single-site, longitudinal, observational research study aims to enroll 70 older veterans with acute TBI who receive computed tomography in the emergency department and 30 matched non-neurotrauma controls who present to the San Francisco VA Medical Center within 14 days of their event. Participants and study partners complete pre-injury health/military relevant exposure assessments and multi-domain geriatric and TBI CDE follow-up assessments at 2 weeks, 3, 6, and 12 months. Blood for proteomic biomarkers is collected at baseline, 6 months, and 12 months. Willing participants also undergo magnetic resonance imaging at 2 weeks, 6 months, and 12 months. This study aims for comprehensive characterization of baseline and longitudinal endophenotypes of an intentionally heterogeneous, "real-world," population of older veterans presenting with acute TBI. Findings will inform the development of future studies focused on optimizing outcomes and evaluating interventions in TBI. This study will provide critical insights into the unique characteristics and the natural history of incident TBI in older veterans, paving the way for larger, Veteran Affairs-based, multicenter prospective studies of acute TBI to inform prevention, support correct diagnosis, and optimize short- and long-term recovery.