A follow-up study of intractable seizures in childhood. One hundred forty-five children with seizures that were refractory to medical therapy for at least 2 years were followed 5 to 20 years after onset. The majority of children with uncontrollable seizures (61%) were mentally retarded, and most of these (73%) had onset of seizures at younger than 2 years of age. Age of onset was significantly later (mean 5.0 +/- 0.5 yr [SEM]) in the group of children with borderline to normal intelligence. Follow-up data showed remission of seizures in a significant proportion of children with borderline or normal intelligence, with a linear decrease of the percentage with persistent seizures at a rate of about 4% per year. Remission of seizures was much less frequent (1.5%/yr) in the group with mental retardation. Seizure type had some effects on outcome. Children with focal atrophic brain lesions did no worse than those without definable pathology on brain-imaging studies. 