The authors report the case of an eight-year-old girl hospitalised for severe headache with paroxysmal left otalgia, vomiting, aprexia, paralysis of the left 6 th cranial nerve and slight left facial weakness. Left carotid arteriography revealed a very large aneurysm of the internal carotid, involving its entire intra-petrous and intra-cavernous course. Treatment consisted of ligation of the internal carotid in the neck. Postoperative angiographic studies showed complete exclusion of the aneurysm, and it was unecessary to carry out "trapping" by ligation of the supra-cavernous carotid, as had initially been envisaged. The postoperative course was uneventful : immediate disappearance of otalgia, secondary complete recovery of the oculo-motor involvement and facial paresis. The absence of any infections or traumatic past history, together with the young age of the patient, represent arguments in favour of the congenital origin of this intra-petrous carotid aneurysm.