Brain malformations are rare congenital anomalies caused by neuronal migration disorders or cerebral tissue destruction during gestation. And epileptic disorders and psychomotor retardation are sometimes induced by them. Previous understanding of these anomalies was derived from pathologic studies after autopsy. The recent advancement of neuroimaging techniques, such as magnetic resonance imaging (MRI), has allowed us to achieve a high diagnostic capability of these malformations. These abnormalities have been more widely recognized morphologically. However, cerebral function in these cases has been rarely described. To evaluate the cerebral functional state in these anomalies, 123I-N-isopropyl-p-iodoamphetamine (123I-IMP) single photon emission computed tomography (SPECT) was performed in 3 cases with brain malformations and 22 normal controls. Several regions of interest (ROI) in the cortex were determined, and the radioactivity at each ROI was counted. The regional cerebral blood flow (rCBF) distribution was evaluated semiquantitatively by calculating the cortico-cerebellar ratios at each ROI. A 23-year-old female with schizencephaly (Case-1) and a 21-year-old male (Case-2) with polymicrogyria showed increased rCBF in their abnormal cortices. And a 39-year-old male with porencephaly (Case-3) demonstrated severely decreased rCBF in his abnormal cortex with gliosis which was considered to be a result from a secondarily disturbed neuronal migration after tissue destruction during gestation. Furthermore, abnormal rCBF distribution was observed in their morphologically normal cortices in addition to their abnormal cortices compared to normal controls. Case-2 showed decreased cerebral perfusion in the morphologically normal cortex around his abnormal cortex with increased rCBF, suggesting surrounding suppression associated with epileptic foci. In contrast, the lesions with decreased rCBF in Case-1 were not around the abnormal cortices. In the cortices with decreased rCBF, despite morphologically normal imaging, of Case-3, the decrement was considered to be diaschisis, since these lesions were located in the ipsilateral hemisphere of the tissue defect. We concluded that brain malformations show various rCBF abnormalities, and these are spread over a larger area than detected by MRI. Therefore, SPECT is a valuable examination method for the determination of abnormal areas and the assessment of pathologic functional state in patients with brain malformations.