The architectonic features of abnormal cerebral cortex in a brain with lissencephaly and pachygyria suggest that neuronal migration was interrupted by cortical and subcortical laminar necrosis in the fourth fetal month. The severest cortical abnormality lies in the distal perfusion fields of the major cerebral arteries, while the normal areas are located in the proximal perfusion fields. These architectonic and topographic features suggest that intra-uterine hypoxia or perfusion failure may be a pathogenetic mechanism leading to lissencephaly and pachygyria.