INTRODUCTION: Traumatic brain injury (TBI) patients are at risk for subsequent TBIs. Research on the longitudinal impact of repetitive TBI is limited. METHODS: The 18-center TRACK-TBI study enrolled subjects who presented to hospital and received head computed tomography (CT) within 24-hours of TBI between 2014-2018. Subjects were interviewed regarding post-index TBI during follow-up. Data from subjects aged = 17-years with 1-year or 3-7-year outcomes were extracted. Outcome measures included functional (GOSE:Glasgow Outcome Scale-Extended), post-concussive symptoms (PCS) (RPQ:Rivermead Post-Concussion Symptoms Questionnaire), psychological distress (BSI-18:Brief Symptom Inventory-18), depression (PHQ-9:Patient Health Questionnaire-9), post-traumatic stress disorder (PCL-5:PTSD-Checklist for DSM-5), and quality of life (QOL) (QOLIBRI-OS:Quality of Life After Brain Injury-Overall Scale). Multivariable regressions were adjusted for demographic, socioeconomic, and injury severity factors, and for multiple comparisons. Mean-differences (B), relative risks (RR), and 95% confidence intervals [CI] were reported. RESULTS: In 1,572 subjects, 3.2% and 12.2% sustained post-index TBI at 1-year and 3-7-years, respectively; 2.4% sustained multiple post-index TBIs at 3-7-years. Risk factors included psychiatric history, prior TBI, and extracranial injury severity. At 1-year, post-index TBI was independently associated with incomplete recovery (GOSE<8; RR = 1.75 [1.04-2.94]), decreased QOL (QOLIBRI-OS: B = -15.9 [-22.6, -9.1]), and increased severity of PCS, psychological distress, PTSD, and depression (RPQ: B = 8.1 [4.2-11.9], BSI-18: B = 5.3 [2.1-8.6]; PCL-5: B = 7.8 [3.2-12.4]; PHQ-9: B = 3.0 [1.5-4.4]); effects were conserved at reduced magnitudes at 3-7-years. Multiple (=2 vs. 1) post-index TBIs were associated with greater symptom severities across all outcome measures. CONCLUSIONS: Post-index TBI is associated with incomplete functional recovery, increased PCS, psychological distress, PTSD, and depressive symptom severities, and decreased QOL at 1- and 3-7-years post-injury. Sustaining multiple post-index TBIs further increases symptom severity across all outcome domains. Institutional processes and resources for TBI prevention, education, counseling, and follow-up are greatly needed.