Recovery from acute disseminated encephalomyelitis in childhood appears relatively uneventful, at least when looking at functional recovery parameters such as neurologic outcome. However, neuropsychology literature suggests that relatively transient illnesses affecting the central nervous system are associated with cognitive and social sequelae, particularly when the illness occurs during the preschool years. This study investigated the impact of timing of acute disseminated encephalomyelitis on intellectual, educational, and social functioning in children. Nineteen children (10 with acute disseminated encephalomyelitis before the age of 5 years), who had been admitted to the Royal Children's Hospital, Melbourne Australia, in the past 6 years underwent a brief neuropsychologic assessment. Performance was compared with 19 control subjects, stratified for age and socioeconomic status with the acute disseminated encephalomyelitis group. Children who sustained their illness before 5 years of age were particularly vulnerable to impairments in both cognitive and social domains. In particular, a higher incidence of severe behavioral and emotional problems was reported by parents of children who had experienced acute disseminated encephalomyelitis before 5 years of age. This finding suggests that there may be long-term complications in early childhood. A multidisciplinary approach to management post-illness is warranted in this age group.