It is currently believed that the ophthalmoplegia in ophthalmoplegic migraine (O.M.) is due to compression of the cranial nerves by dilated and swollen carotid or basilar arteries. One of our patients seen recently did not fit the pattern of a compressive neuropathy because the pupil was spared during three episodes of O.M. A review of the literature revealed that contrary to common belief, the pupils are involved completely in only 33% of patients with O.M. Analysis of the clinical features and the relevant anatomy of the vascular supply of the third cranial nerve suggest that the ophthalmoplegia is due to a delayed ischemic neuropathy leading to border zone infarction of the nerve rather than direct compression due to an enlarged vessel.