ABSTRACT: Importance:After traumatic brain injury (TBI), children often experience impairment when faced with tasks and situations of increasing complexity. Studies have failed to consider the potential for attention problems to develop many years after TBI or factors that may predict the development of secondary attention-deficit/hyperactivity disorder (SADHD). Understanding these patterns will aid in timely identification of clinically significant problems and appropriate initiation of treatment with the hope of limiting additional functional impairment. Objective:To examine the development of SADHD during the 5 to 10 years after TBI and individual (sex, age at injury, and injury characteristics) and environmental (socioeconomic status and family functioning) factors that may be associated with SADHD. Design, Setting, and Participants:Concurrent cohort/prospective study of children aged 3 to 7 years hospitalized overnight for TBI or orthopedic injury (OI; used as control group) who were screened at 3 tertiary care children's hospitals and 1 general hospital in Ohio from January 2003 to June 2008. Parents completed assessments at baseline (0-3 months), 6 months, 12 months, 18 months, 3.4 years, and 6.8 years after injury. A total of 187 children and adolescents were included in the analyses: 81 in the TBI group and 106 in the OI group. Main Outcomes and Measures:Diagnosis of SADHD was the primary outcome. Assessments were all completed by parents. Secondary ADHD was defined as an elevated T score on the DSM-Oriented Attention-Deficit/Hyperactivity Problems Scale of the parent-reported Child Behavior Checklist, report of an ADHD diagnosis, and/or current treatment with stimulant medication not present at the baseline assessment. The Family Assessment Device-Global Functioning measurement was used to assess family functioning; scores ranged from 1 to 4, with greater scores indicating poorer family functioning. Results:The analyzed sample included 187 children with no preinjury ADHD. Mean (SD) age was 5.1 (1.1) years; 108 (57.8%) were male, and 50 (26.7%) were of nonwhite race/ethnicity. Of the 187 children, 48 (25.7%) met our definition of SADHD. Severe TBI (hazard ratio [HR], 3.62; 95% CI, 1.59-8.26) was associated with SADHD compared with the OI group. Higher levels of maternal education (HR, 0.33; 95% CI, 0.17-0.62) were associated with a lower risk of SADHD. Family dysfunction was associated with increased risk of SADHD within the TBI group (HR, 4.24; 95% CI, 1.91-9.43), with minimal association within the OI group (HR, 1.32; 95% CI, 0.36-4.91). Conclusions and Relevance:Early childhood TBI was associated with increased risk for SADHD. This finding supports the need for postinjury monitoring for attention problems. Consideration of factors that may interact with injury characteristics, such as family functioning, will be important in planning clinical follow-up of children with TBI.