We report here a case of giant internal carotid artery (ICA) pseudoaneurysm as a complication of transsphenoidal surgery. This 50-year-old acromegalic male presented to our clinic with a status of hypovolemic shock due to serious epistaxis. Neuroradiological examinations at his admission revealed a giant aneurysm in the right cavernous portion projecting into the sphenoid sinus. Eight years before this presentation, he had undergone a transsphenoidal surgery for growth hormone producing pituitary tumor at the other clinic. Then intraoperative arterial bleeding was reported, probably as a result of carotid injury. His medical history and radiological findings suggested that his epistaxis resulted from a rupture of the iatrogenic pseudoaneurysm which had gradually grown after the ICA injury at the previous surgery over 8 years. Emergent coil embolization using Guglielmi detachable coils (GDCs) resulted in a successful homeostasis. Major part of the aneurysm dome was obliterated via the intervention, however small part of the aneurysm neck was unable to be obliterated due to a technical difficulty. His postoperative course was favorable, but he suffered from a recurrence of serious epitaxis 4 weeks after the embolization. Emergent angiography suggested a rupture of the un-obliterated aneurysm neck remnant. Thus, trapping of the aneurysm combined with high flow bypass was necessitated. Relevant literatures are reviewed, and possible therapeutic strategies for this rare lesion are discussed.