An infant of a diabetic mother lived 13 days after birth. She had a small dysplastic 12.6 gm. brain, partly forming a frontal encephalocele. The uncleaved forebrain contained a mass of poorly organized heterotopic cerebellar cortex. The cerebellum itself had normal lamination, but was small and continuous with the dysplastic tissue. The ventricular system was absent except for a few midline ependymal rosettes, and the cerebral cortex was not developed. The cerebellar dysplasia resembled a proliferative and invasive lesion by its rostral extension.