Objective To characterize and compare subgroups of survivors with assault-related versus self-inflicted traumatic brain injuries (TBIs) via firearms at the time of inpatient rehabilitation and at 1-, 2-, and 5-year follow-up. Design Secondary analysis of data from the Traumatic Brain Injury Model Systems National Database (TBIMS NDB), a multicenter, longitudinal cohort study. Setting Retrospective analyses of a subset of individuals enrolled in the TBIMS NDB. Participants Individuals 16 years and older (N=399; 310 via assault, 89 via self-inflicted injury) with a primary diagnosis of TBI caused by firearm injury enrolled in the TBIMS NDB. Interventions Not applicable. Main Outcome Measures Disability Rating Scale, Glasgow Outcome Scale–Extended, sociodemographic variables (sex, age, race, marital status), injury-related/acute care information (posttraumatic amnesia, loss of consciousness, time from injury to acute hospital discharge), and mental health variables (substance use history, psychiatric hospitalizations, suicide history, incarcerations). Results Individuals who survived TBI secondary to a firearm injury differed by injury mechanism (assault vs self-inflicted) on critical demographic, injury-related/acute care, and mental health variables at inpatient rehabilitation and across long-term recovery. Groups differed in terms of geographic area, age, ethnicity, education, marital status, admission Glasgow Coma Scale score, and alcohol abuse, suicide attempts, and psychiatric hospitalizations at various time points. Conclusions These findings have implications for prevention (eg, mental health programming and access to firearms in targeted areas) and for rehabilitation planning (eg, by incorporating training with coping strategies and implementation of addictions-related services) for firearm-related TBI, based on subtype of injury.