To examine the relative contributions of injury severity, level of physical and cognitive disability, child behavior and family function to short-term outcome 6 months following traumatic brain injury (TBI) in children.Prospective, longitudinal, between-group design, comparing preinjury and postinjury measures of functional outcome across three levels of injury severity.One hundred and twelve children, aged 2-12 years admitted to the Royal Children's Hospital, Melbourne, with a diagnosis of TBI. The sample was divided into three groups, according to injury severity: mild TBI (n = 31), moderate TBI (n = 52) and severe TBI (n = 29). Children with a history of neurologic, developmental and psychiatric disorder were excluded from participation.Levels of postinjury functioning in the following domains: physical function, cognitive ability (incorporating intellect, memory and attention), behavioral and family functioning, and level of family burden.A clear dose-response relationship for physical and cognitive outcomes was found, with severe TBI associated with greater impairment of physical, intellectual, memory and attentional function. For psychosocial outcome, results were less clearly linked to injury severity. Preinjury behavioral and family functioning were closely related to postinjury function in these domains, with an interaction identified between family function and child behavior at 6 months postinjury. Family functioning remained unchanged postinjury, although level of burden was high, and predicted by injury severity, functional impairment and postinjury behavioral disturbance.These results suggest ongoing functional problems for the child and significant family burden 6 months following TBI. The nature and severity of physical and cognitive problems are most closely related to injury severity, with family functioning and child behavior better predicted by psychosocial and premorbid factors.