Objective: To assess the phenomenology and predictive factors of attention-deficit/hyperactivity disorder (ADHD) after traumatic brain injury (TBI), also called secondary ADHD (SADHD). Method: Children without preinjury ADHD 5-14 years old with TBI from consecutive admissions (n = 143) to five trauma centers were observed prospectively for 6 months (baseline and 6 months), with semistructured psychiatric interviews. Injury severity, lesion characteristics, and preinjury variables including psychiatric disorder, family psychiatric history, family psychiatric history of ADHD, family function, socioeconomic status, psychosocial adversity, and adaptive function were assessed with standardized instruments. Results: SADHD in the first 6 months after injury occurred in 18 of 115 (16%) of returning participants. All subtypes of ADHD occurred. Socioeconomic status (p = .041) and orbitofrontal gyrus lesions (p = .005) independently significantly predicted SADHD. Conclusions: These findings are consistent with research on developmental ADHD that implicate psychosocial factors and prefrontal structural and functional differences between those with and without the disorder.