The present study investigated the associations between CT measures and obstetric complications and family history of major mental illnesses. We had the hypothesis of diosthesis-stress model in the etiology of schizophrenia. We had the following findings. 1) Family history of major mental illnesses is inversely related to obstetric complications. 2) Prefrontal sulcal widening and family history of schizophrenia. are inversely related. 3) In female but not in male patients those with family history of schizophrenia tended to have less prefrontal sulcal widening and ventricular brain ratio. These results suggest that more genetic factors contribute to structural brain abnormalities in female than in male patients.