In comparison with age-matched groups who sustained mild to moderate head injury, children and adolescents with severe head injury initially exhibited memory deficit. Cognitive impairment persisted primarily in the severely injured children, whereas the follow-up performance of severely injured adolescents more closely approximated that of age-matched patients with mild or moderate head injury. The results suggest that young children are no less and may be even more vulnerable to the deleterious effects of diffuse injury on memory and cognition.