Two children with autism and Klinefelter syndrome (KS) (47, XXY) are presented. Both qualify for the diagnosis of autism based on DSM-IV with severely delayed and disordered language, difficulties with social interaction, and a restricted range of interests and activities. Both also have abnormal EEGs, and one patient has had what appear to be clinical seizures. Trials of antiepileptic medications have not been beneficial in either patient. We report the clinical and EEG findings of each patient, and discuss the implications of this combination of disorders.