The overall goal of our study is to estimate the 5-year incidence of late-onset epilepsy in a population-based cohort of children and young adults who sought medical care after traumatic brain injury (TBI). Secondarily, we will identify risk factors and biomarkers for onset of epilepsy. From this study, we may establish additional cohorts that can benefit from acute therapies after TBI, and broaden the inclusion criteria in future clinical trials investigating therapies to modify epileptogenesis after TBI.