Traumatic brain injury (TBI) is more common among youths involved in the juvenile justice system than the general pediatric population; the estimated rate of TBI in this population is as high as 30%. • The neurobiologic effects of TBI depend on the severity of impact; in general, TBI is characterized by hematomas and diffuse axonal injury (DAI), leading to disrupted axonal transport and neuronal circuits. • Evidence supporting a direct causal relationship between TBI in youths and criminality include the high prevalence of executive functioning deficits among youths with TBI, a dose-dependent relationship between frequency of self-reported TBI and degree of violence in offenses, and between severity of TBI and age at first offense. In addition, TBI is associated with increased risk of disruptive behavioral disorders and substance use, which increases risk of criminality. • However, a direct causal relationship between TBI and criminality among youths has not been established; specifically, adolescents may be predisposed to risk-taking behavior that predates their TBI because of environmental (e.g., violence at home) and biological (e.g., genetic loading for risk-taking behavior) factors.