Abstract Objective: To study adaptive functioning after severe traumatic brain injury (TBI). Design: Case-control study. Setting: A university hospital and three regional and four community hospitals. Subjects: A consecutive series ( n = 24) of children age 5 through 14 years who suffered severe TBI were individually matched to subjects who sustained a mild TBI and to a second group who sustained an orthopedic injury with no evidence of TBI. Main Outcome Measures: Standardized adaptive functioning, intellectual, psychiatric, and neuroimaging assessments were conducted on average 2 years after injury. Results: Severe TBI was associated with significantly ( p < .05) lower Vineland Adaptive Behavior composite, communication, and socialization standard scores and lower Child Behavior Checklist parent-rated social competence scores compared with children with orthopedic injury. Severe TBI and mild TBI subjects were significantly ( p < .05) more impaired than orthopedic subjects on teacher-rated adaptive function. Family functioning, psychiatric disorder in the child, and IQ were significant variables, explaining between 22% and 47% of the variance in adaptive functioning outcomes. Conclusions: Severe TBI is associated with significant deficits in child adaptive functioning. This association appears to be mediated by family dysfunction, child psychiatric disorder, and intellectual deficits.