PURPOSE: Concussion has been associated with disturbance of physical well-being, thought process, and emotions, that may last 6 months or longer after the time of injury. Homeless adolescents are at higher risk for brain injury than adolescents from safer environments due to increased behaviors leading to injury. Impulsivity and affective liability are part of the DSM-IV definition of Postconcussional Disorder, These attributes have also been noted to be more common in homeless youth. We hypothesized an association between previous head injury and impulsivity and behavioral dyscontrol, as possible symptoms of postconcussional disorder. METHODS: Homeless adolescents accessing services at a shelter were surveyed about health histories, including the statement``Have you ever been hit on the head so hard you lost consciousness''. In the same survey a psychologic symptom battery, the SCL-90, was administered, The incidence of head injury was then compared with psychiatric symptom indices in the highest quartile. An odds ratio for the severity of psychologic symptoms in those with history of concussion was then calculated. RESULTS: Of the 97 youth interviewed, 38 endorsed a history of grade III concussion, generating a prevalence of brain injury which is 40% higher than that reported in one study of high school football players. Odds ratios for psychiatric symptom score in the 75h percentile or greater among those with history of grade III concussion were as follows: