Objective: A previous study conducted by our group found theory of mind (ToM) differences in preschool children who sustained mild traumatic brain injury (mTBI) compared with typically developing peers, 6 months postinjury. The goals of the current longitudinal study were to determine whether these findings are the result of a brain-injury-specific effect or rather a general-injury effect, to examine the long-term evolution of ToM skills following preschool mTBI, as well as to investigate the links between ToM abilities and general social functioning. Method: Seventy-two children who sustained mTBI between the ages of 18 and 60 months were evaluated 6 and 18 months postinjury on ToM tasks including desires and emotions reasoning and false belief understanding. They were compared with 58 participants who sustained an orthopedic injury (OI) and 83 typically developing children (TDC). Results: The 3 groups did not differ on demographic and baseline characteristics. The mTBI group obtained poorer scores relative to both comparison groups on the desires and emotions reasoning task, both at 6 and 18 months injury. No correlations were found between injury characteristics and ToM performance. For the mTBI group, associations were found between ToM performance and global social competence. Conclusion: These findings suggest a brain-injury-specific effect that persists in the long-term following mTBI in preschool children.