The authors report a case of alternating hemiplegia (AH) in a 3yr 6m old boy who had presented, from the age of 4 months on, episodes of alternating hemi- or quadriplegia. Brainstem auditory evoked potentials were recorded both in the interictal state and, for the first time, during an attack. There was no significant difference between the two states. These findings suggest that a massive involvement of the posterior vascular territory is not likely to be associated with attacks in AH.