To determine seizure propagation patterns, we analyzed ictal positron emission tomography (PET) studies of regional cerebral glucose utilization in 18 children (11 male and 7 female aged 2 weeks to 16 years) with epilepsy (excluding infantile spasms IS). Three major metabolic patterns were determined based on degree and type of subcortical involvement: Nine children had type I; asymmetric glucose metabolism of striatum and thalamus. Of these, the 7 oldest children showed unilateral cortical hypermetabolism (always including frontal cortex) and crossed cerebellar hypermetabolism. Two infants (aged < 1 year) had a similar ictal PET pattern but no cerebellar asymmetry, presumably owing to immaturity of corticopontocerebellar projections. Five children had type II, symmetric metabolic abnormalities of striatum and thalamus; this pattern was accompanied by hippocampal or insular cortex hypermetabolism, diffuse neocortical hypometabolism, and absence of any cerebellar abnormality. Four children had type III, hypermetabolism restricted to cerebral cortex. This classification can accommodate ictal PET and single photon emission computed tomography (SPECT) patterns described by other investigators. Future studies should be directed at the clinical relevance of this classification, particularly with regard to epilepsy surgery.