Objective: The impact of traumatic brain injury (TBI) extends beyond the person who was injured. Family caregivers of adults with moderate to severe TBI frequently report increased burden, stress and depression. Few studies have examined the well-being of family members in the mild TBI population despite the latter representing up to 95% of all TBIs. Methods: Five areas of well-being were examined in 99 family members (including parents, partners, siblings, other relatives, adult children, friends or neighbours) of adults (aged >= 16 years) with mild TBI. At 6- and 12-month post-injury, family members completed the Bakas Caregiver Outcomes Scale, Short Form-36 Health Survey, EQ-5D-3L, Hospital Anxiety and Depression Scale and the Pittsburgh Sleep Quality Index. Outcomes and change over time and associated factors were examined. Results: At 6 months, group mean scores for health-related quality of life for mental and physical components and overall health status were similar to the New Zealand (NZ) population. Mean scores for sleep, anxiety and depression were below clinically significant thresholds. From 6 to 12 months, there were significant improvements in Bakas Caregiver Outcomes Scale scores by 2.61 (95% confidence interval: 0.72-4.49), health-related quality of life (mental component) and EQ-5D-3L overall health (P= 0.01). Minimally clinically important differences were observed in overall health, anxiety, health-related quality of life and depression at 12 months. Female family members reported significant improvements in physical health over time, and more positive life changes were reported by those caring for males with TBI. Conclusions: The findings suggest diminished burden over time for family members of adults with mild TBI.