A case is presented of neurilemmoma of the left oculomotor nerve occurring in a 64-year-old hypertensive woman. The incipient tumour produced ptosis, limited inwards rotation of the eyeball, and persistent pupillary dilatation on the left side. The mechanism of this process is discussed, having regard to the interruption of the fibres innervating these structures by the tumour, and considering the mode of occurrence of the ocular and pupillary impairments. The patient also had generalized athero-sclerosis and fusiform aneurysm of the terminal part of the left internal carotid artery. The symptoms of headache, seizure, coma, and temporary right hemiparesis were considered as manifestations of hypertensive encephalopathy unrelated to the tumour.