Turner's syndrome (TS) is rarely associated with serious abnormalities of brain structure or malformations of cortical development. We report a 17-year-old girl with TS and 45,XO/46,XX mosaicism presenting bilateral frontal polymicrogyria (BFP) and epilepsy. To our knowledge, the association between TS and BFP has never been reported to date. Our observation confirms that in humans the X-chromosome plays an important role in the development and specialization of brain structure and function. We hypothesize that the absence or abnormalities of developmental genes localized on the X-chromosome could be involved in the pathogenesis of BFP observed in our patient.