Purpose: To investigate the psychosocial impact of TBI on siblings and to identify the factors associated with their psychosocial functioning. Methods: A systematic search of six databases (CINAHL, Medline, Scopus, PsychINFO, Web of Science and Embase) was conducted from 1980 to May 1st, 2020. Studies involving siblings of a child or adult with TBI that employed validated self-report measures of psychosocial functioning were included. Quality of methodology was appraised by two reviewers. Results: Thirteen articles were identified, reporting on 11 cross-sectional studies. Although there were mixed findings overall, siblings typically reported greater mood symptoms and distress related to family functioning as compared to the norms and control samples. Siblings’ psychosocial functioning was comparable to other family members, although they were less likely to be primary caregivers. Having a brother or sister with behavioural problems and low levels of social support were the factors most consistently related to poor psychosocial functioning in siblings. Conclusions: Siblings of individuals with TBI may experience negative changes in psychosocial functioning. They are at greater risk of poor psychosocial functioning when their brother or sister with TBI has behavioural problems and when they perceive low social support. Longitudinal studies on siblings’ adjustment trajectory over time and research on support interventions for siblings are recommended.Implications for Rehabilitation Traumatic brain injury can have a negative impact on siblings’ psychosocial functioning with respect to mood and distress related to family functioning. As siblings experience similar impacts on their psychosocial functioning to other family members, specific focus on their adjustment to role changes may be needed. Siblings with a brother or sister with behavioural problems and those perceiving lower social support may particularly benefit from monitoring and support.