Clinical and electrographic seizures were recorded in an infant with atelencephaly. Because the infant had no cerebral hemispheres, the ictal discharges were presumed to arise from the disorganized diencephalic derivatives that occupied the entire supratentorial space. The case provided strong support for the concept that, unlike epileptic seizures in older patients, some types of neonatal seizures may originate and propagate exclusively in subcortical structures. This may explain the striking dissociation between the electrographic and behavioral aspects of seizures occasionally observed in newborns, as well as the frequent intractability of such seizures to standard anticonvulsants.