This study investigated the association between mild traumatic brain injury (mTBI) and ADHD, which increases risk of injuries and accidents. We conducted a systematic review and meta-analysis of studies that examined the relationship between mTBI and ADHD. Five studies, comprising 3,023 mTBI patients and 9,716 controls, fit our a priori inclusion and exclusion criteria. A meta-analysis found a significant association between ADHD and mTBI, which was significant when limited to studies that reported on ADHD subsequent to mTBI and when the direction of the association was not specified, but not for studies that reported mTBI subsequent to ADHD. Heterogeneity of effect size and publication biases were not evident. The literature documents a significant association between mTBI and ADHD. Further clarification of the relationship and direction of effect between mTBI and ADHD and treatment implications could have large clinical, scientific, and public health implications.