Electrophysiological studies were performed on two children with hydranencephaly that was diagnosed by CT and/or magnetic resonance imaging (MRI). Case 1 was a 4-months-old boy who had no rostral tissue above the midbrain. Case 2 was a 5-years-old boy in whom CT showed the presence of the thalamus. Short latency somatosensory evoked potentials (SSEP) in both cases exhibited the absence of cortical activity (N1 and P4) with the preservation of waves of brainstem origin. However, in case 1, the wave component N0 was not observed, while N0 was seen in case 2. Thus, the N0 was component of SSEP on median nerve stimulation in children, which corresponds to N16 in adults, may originate in the thalamus.