A case of extensive classical four layered cerebral microgyria was examined in whole brain serial section using routine cell and fiber stains, and in Golgi impregnations. Golgi preparations demonstrate that microgyric cortex contains the spectrum of neurons characteristically found in normal cortex, and that they are segregated by class into horizontal laminar comparable to layers I--VI in the normal. In microgyric cortex neurons of the mid-cortical layers, variably layers II--V, are replaced by a tangential band of fibrous astrocytes. These findings confirm impressions from general cell and fiber stains that classical four layered microgyria is the result of a destructive process striking predominantly in mid-cortical regions. It must occur after migration is complete but before the development of secondary and tertiary gyri, that is, between the fifth and seventh fetal months. The cellular pathology as seen in Golgi impregnations establishes that neurons surviving above the scar are normally differentiated, aligned, and oriented. By exception, many surviving neurons at the border of the scar have attenuated dendritic arbors which are oriented tangentially. Very few axons or dendrites actually traverse the scar.