OBJECTIVE 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. METHODS Postconcussional symptomatology, behavior ratings, and neuropsychological test performance were examined at 1 week and 3 months postinjury. METHODS Participants were recruited from successive presentations to emergency departments of two major hospitals. METHODS 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.