A dysplastic neuronal lesion of the floor of the fourth ventricle (DNFFV) causes hemifacial seizures (HFS) from early infancy. However, it is still controversial whether HFS is generated by the facial nerve nucleus or cerebellar cortex. In this study, we confirm a direct correlation between the rhythmic activities in the DNFFV and HFS using intraoperative electroencephalography (EEG) and electromyography (EMG) monitoring. Our results support the theory that a DNFFV provokes ipsilateral HFS via the facial nerve nucleus.