The histological features of cerebellar microgyria are described in a 15 month old infant. The bizarre appearance of this malformation seems to be the result of two basic factors: secondary fusion between preformed folia, and deficient and disorderly formation of the internal granule cell layer. The findings support the view according to which cerebellar microgyria is probably due to a pathological process involving the external granule cell layer during a relatively late period of cerebellar development.