Objectives:To investigate outcome in children with mild traumatic head injury (THI) at 1 week and 3 months postinjury and to identify factors associated with persisting problems.Design:Postconcussional symptomatology, behavior ratings, and neuropsychological test performance were examined at 1 week and 3 months postinjury.Setting:Participants were recruited from successive presentations to emergency departments of two major hospitals.Participants:130 Children with mild THI were compared with 96 children having other minor injuries as controls.Results:Children with mild THI experienced headaches, dizziness, and fatigue but exhibited no cognitive impairments, relative to controls, at 1 week postinjury. By 3 months, symptoms had resolved. However, 17% of children showed significant ongoing problems. They were more likely to have a history of previous head injury, learning difficulties, neurological or psychiatric problems, or family stressors.Conclusions:Persisting problems following mild head injury in children are more common in those with previous head injury, preexisting learning difficulties, or neurological, psychiatric, or family problems. These “at-risk” children should be identified in the emergency department and monitored.