ObjectiveTo examine the association between severity of traumatic brain injury (TBI) as measured by duration of post-traumatic amnesia (PTA) and first year hospitalization costs for service members and veterans (SMVs) treated for TBI at Polytrauma Rehabilitation Centers (PRCs) within the Veterans Health Administration (VHA). DesignMultivariable models of merged datasets from the VA TBI Model Systems (VA TBIMS) national database containing TBI clinical characterization including PTA with VHA hospital cost data. SettingFive VA PRCs. ParticipantsVA TBIMS participants with known PTA who received inpatient rehabilitation within 1 year of their TBI at any of 5 PRCs between 2010 and 2020 (N=717). InterventionsN/A. Main Outcome MeasuresTotal, acute care, rehabilitation, intensive care unit (ICU), and surgery costs across all VA hospitals. ResultsA total of 717 SMVs (mean age 36.9 years, 94.1% men, 76.8% non-Hispanic White, 7.8% active duty) met inclusion criteria for the unadjusted analyses. Unadjusted mean total hospital costs in the first-year post TBI were approximately $201,214 higher for those with PTA duration ≥24 hours ($351,157) than PTA <24 hours ($149,943). In adjusted models (n=583), each additional day of PTA duration incrementally increased total ($1453), rehabilitation ($1324), ICU ($78), and surgery ($39) costs. Other significant covariates included age, acute care length of stay, Disability Rating Scale on rehabilitation admission, penetrating violent cause of injury, and drug abuse. ConclusionsThis study demonstrates that PTA as a quantitative measure of TBI severity significantly affects first-year hospitalization costs of SMVs treated at PRCs. Each additional day of PTA was associated with higher total, rehabilitation, ICU, and surgery costs. Mean first year hospital costs were also found to exceed the highest budget allocation to VHA facilities for a veteran treated at a PRC. These findings have possible implications for hospital care provision for those receiving inpatient rehabilitation in VHA settings.