Pupillary dilatation was observed in a young boy who had a sudden onset of right focal seizures. Clinical and laboratory investigation revealed the presence of a benign left frontal epileptic focus. Lacking signs of third cranial nerve compression, this transient pupillary abnormality could be caused by the contralateral frontal epileptic focus. Such a focus might inhibit dilatation of the homolateral pupil, thus permitting dilatation of the contralateral pupil only. Unilateral mydriasis as described hereby could also represent a pupillary "Todd's Paralysis" caused by the contralateral frontal epileptic focus.