In contrast to neoplasia, lesions of focal cerebral dysplasia are thought to be completed developmental processes of abnormal neuronal migration. We present three children with seizures resulting from brain lesions which pathologically demonstrate regions of both clearcut focal cortical dysplasia and also hypercellularity and monomorphism typical of proliferative lesions such as low grade glial tumor. These cases suggest the existence of a distinct subgroup of patients with prominent glioproliferative changes in association with focal cortical dysplasia, challenging the conventional dichotomy between dysplastic and proliferative categories of brain lesions. Recognition of patients with dual pathology may be of practical as well as theoretical importance.