We examined 2 siblings with schizencephaly. A 23-year-old female (Case-1) had a mild left hemiparesis, and her 25-year-old brother (Case-2) presented a quadriplegia. Both cases achieved a borderline intellectual level and both had seizure disorders. The magnetic resonance imaging (MRI) of Case-1 revealed thickened gray matter around the fused schizencephalic clefts in the bilateral frontal lobes, mild ventricular enlargement and absence of the septum pellucidum. And, the MRI result of Case-2 disclosed similar but more severe abnormalities. The positron emission tomography (PET) using 18F-Fluoro-2-deoxy-D-glucose of Case-1 demonstrated focal hypermetabolic activity in the ectopic gray matter with the absence of epileptic discharges on the electroencephalogram on the day of PET study. And the single photon emission computed tomography (SPECT) using 123I-N-isopropyl-p-iodoamphetamine of Case-1 delineated focal hyperperfusion in the same lesions. The PET and SPECT findings are unique, since previous reports have indicated focal hypoperfusion and hypometabolism in abnormal gray matter. Familial schizencephaly is a very rare malformation, and this is the first report of that in Japan. Further evaluation in similar cases is needed to determine the pathophysiology of this anomaly.