We report a case of idiopathic rupture of an internal carotid artery (ICA) aneurysm in an infant, a finding that we believe has not been previously reported in the literature. The more common causes of isolated injury to the ICA are deep neck space infections and penetrating intraoral trauma. Pseudoaneurysms of the artery are well known to result in delayed hemorrhage. In most cases, the outcome is unfavorable because of the large amount of blood loss. Our case involved a previously healthy 11-month-old girl who presented with massive epistaxis secondary to a ruptured left ICA aneurysm. The patient had no history of any antecedent trauma or infection. She was successfully managed by ligation of the involved ICA in the neck.