As part of an autopsy research project, the brains of four autistic subjects were examined and compared with those of three comparison subjects without CNS pathology and one with phenytoin toxicity. The cerebellum was selected for initial investigation because pathognomonic symptoms and neurophysiological measures suggest that pathology may exist in the cerebellar-vestibular axis in certain patients. Total Purkinje cell counts were significantly lower in the cerebellar hemisphere and vermis of each autistic subject than in the comparison subjects.