Background:We evaluated the risk of attention-deficit hyperactivity disorder (ADHD) following childhood traumatic brain injury (TBI). Methods: Using Taiwan's National Health Insurance Research Database, we included 10,416 newly diagnosed TBI children (aged ≤12 y) between 2001 and 2002 and 41,664 children without TBI, who were frequency matched by sex, age, and year of the index medical service with each TBI child, as controls. Children who had been diagnosed with ADHD prior to their medical service index were excluded. Each individual was followed for 9 y to identify ADHD diagnosis. We also compared the ADHD risk in children who were treated for fractures but not TBI as sensitivity analysis. results: During the 9-y follow-up period, children with TBI had a higher ADHD risk (adjusted hazard ratio (AHR) = 1.32, 95% confidence interval (CI) = 1.19, 1.45) than did those without TBI. Furthermore, children with mild and severe TBI had higher AHRs for ADHD than did those without TBI (AHR = 1.30; 95% CI = 1.10, 1.53; and AHR = 1.37; 95% CI = 1.22, 1.55). However, no significant association was observed between fractures and ADHD. conclusion: TBI in childhood is associated with a greater likelihood of developing ADHD. t raumatic brain injury (TBI) is the leading cause of death and disability in children and often results in persistent behavioral disturbances and neurocognitive deficits in attention, learning, and memory (1-3). Children with cognitive impairment following TBI impose a great economic and social burden on their families and communities. In addition, these children are more likely to have slower psychosocial development and exhibit poor academic achievement. Therefore, the relationship between TBI and neuropsychiatric consequences has become a crucial research topic.Attention-deficit-hyperactivity disorder (ADHD), a neurodevelopmental disorder, is associated with impulsivity, excessive talking, difficulty in sustaining attention, being easily distracted, and injuries (4-6). Studies have reported a relationship between ADHD and childhood TBI (7-10). Unlike other diseases resulting from various pathogenic mechanisms, TBI is caused by a complex interplay among damages occurring in the neuroanatomy, neurochemistry, and neurophysiology because of primary and secondary processes (11). A meta-analytic review showed that neurocognitive outcomes after pediatric TBI have a dose-response relationship with injury severity. Babikian and colleagues found that patients with severe TBI exhibited poorer performance in intelligence quotient tests, executive functioning, processing speed, attention maintenance, verbal immediate memory, and delayed memory, whereas patients with mild TBI exhibited no change (12). In addition, several studies have suggested that children with moderate to severe TBI are significantly more likely to develop ADHD symptoms than are those with mild TBI (8,(13)(14)(15)(16)(17). A longitudinal birth cohort study reported no association between preschool mild TBI and ADHD after adjusting for potential co...