About 63% of all traumatic brain injuries (TBI) occur in teenagers and adults aged 15-64 years, the primary working population. Since reports of failure to return to work (FTRTW) vary, understanding the factors that influence FTRTW is key to improving work outcomes for this primarily working-age population. Our study sample consists of 343 previously employed persons who were hospitalized following TBI and had either returned to work at 1 year or had failed to return to work because of their injury (injury-related FTRTW). Medical records were reviewed and participants were interviewed by telephone at 1 year post-discharge. Individuals with injury-related FTRTW were far more likely to report dependence or modified independence on the Functional Independence Measure (FIM) than those who were employed at 1 year. The joint distribution of motor and cognitive items suggests that, for a given level of cognitive function, the addition of a motor limitation will result in greater injury-related FTRTW. In addition as motor function declines, FTRTW is further increased. Injury-related FTRTW is also associated with being unmarried and not completing high school. While the importance of behavioural, economic, and psychosocial factors should not be minimized, services aimed at improving function can be expected to have an impact on RTW after TBI.