Objective: To investigate recovery of medical decision-making capacity (MDC) over 6 months in persons with traumatic brain injury (TBI) stratified by injury severity. Design: Longitudinal study comparing controls and patients with TBI 1 month after injury (t1) and 6 months after injury (t2). Setting: Inpatient TBI rehabilitation unit and outpatient neurology department. Participants: Participants (N=151) consisted of control subjects (n=60) and patients with TBI (n=91) stratified by injury severity: mild TBI (mTBI; n=27), complicated mild TBI (cmTBI; n=20), and moderate/severe TBI (msevTBI; n=44). Interventions: Not applicable. Main Outcome Measures: We used the Capacity to Consent to Treatment Instrument to evaluate MDC performance on 5 consent standards (expressing choice, reasonable choice, appreciation, reasoning, and understanding). We also assigned capacity impairment ratings on the consent standards to each participant with TBI using cut scores referenced to control performance. Results: Control performance was stable across time on the consent standards. Patients with mTBI and cmTBI performed below controls on the understanding standard at t1 but not t2. Patients with msevTBI performed below controls on appreciation, reasoning, and understanding at t1, and on appreciation and understanding at t2, but showed substantial improvement over time. Conclusions: Regardless of injury severity, all groups with TBI demonstrated baseline impairment of MDC with subsequent partial or full recovery of MDC over a 6-month period. However, a sizeable proportion of individual patients with TBI in each group continued to demonstrate capacity compromise at 6 months postinjury. Clinically, this finding suggests that individuals with TBI, regardless of injury severity, need continued monitoring regarding MDC for at least 6 months after injury.