Traumatic brain injury (TBI) is a global health priority, associated with substantial burden. Historically conceptualised as an injury event with finite recovery, TBI is now recognised as a chronic condition that can affect multiple domains of health and function, some of which might deteriorate over time. Many people who have had a TBI remain moderately to severely disabled at 5 years, are rehospitalised up to 10 years post-injury, and have a reduced lifespan relative to the general population. Understanding TBI as a chronic disease process can be highly informative for optimising care, which has traditionally focused on acute care. Chronic brain injury care models must be informed by a holistic understanding of long-term outcomes and the factors that can affect how care needs evolve over time. The United States Traumatic Brain Injury Model Systems of Care follows up individuals with moderate-to-severe TBI for over 30 years, allowing characterisation of the chronic (2-30 years or more post injury) functional, cognitive, behavioural, and social sequelae experienced by individuals who have had a moderate-to-severe TBI and the implications for their health and quality of life. Older age, social determinants of health, and lower acute functional status are associated with post-recovery deterioration, while younger age and greater functional independence are associated with risky health behaviours, including substance misuse and re-injury. Systematically collected data on long-term outcomes across multiple domains of health and function are needed worldwide to inform the development of models for chronic disease management, including the proactive surveillance of commonly experienced health and functional challenges.