OBJECTIVE To determine the relationship between adult-onset traumatic brain injury (TBI) and social functioning including employment, social relationships, independent living, recreation, functional status, and quality of life 6 months or longer after injury. METHODS Not applicable. METHODS Systematic review of the published, peer-reviewed literature. METHODS Not applicable. RESULTS Fourteen primary and 25 secondary studies were identified that allowed comparison to controls for adults who were at least 6 months post-TBI. TBI decreases the probability of employment after injury in those who were workers before their injury, lengthens the timing of their return if they do return to work, and decreases the likelihood that they will return to the same position. Those with moderate and severe TBI are clearly affected, but there was insufficient evidence of a relationship between unemployment and mild TBI. Penetrating head injury sustained in wartime is clearly associated with increased unemployment. TBI also adversely affects leisure and recreation, social relationships, functional status, quality of life, and independent living. Although there is a dose-response relationship between severity of injury and social outcomes, there is insufficient evidence to determine at what level of severity the adverse effects are demonstrated. CONCLUSIONS TBI clearly has adverse effects on social functioning for adults. While some consequences might arise from injuries to other parts of the body, those with moderate to severe TBI have more impaired functioning than do those with other injuries alone.