Mycotic aneurysm of external carotid artery is extremely rare. We herein report a case of external carotid artery (ECA) aneurysm following severe traumatic brain injury. A 24-year-old man with severe traumatic brain injury (TBI) following a car accident was referred to Rajaee Trauma Center Emergency Room affiliated to Shiraz University of Medical Sciences in Shiraz, Iran. He underwent ventriculostomy on arrival for intracerebral pressure (ICP) monitoring and for a second time due to hydrocephalus following decompressive craniectomy. He developed fulminant meningitis and ventriculitis during his hospital course. A bulged pulsatile lesion under the frontotemporal scalp resulted into the suspicion to underlying vascular pathology. Six-vessel angiography of brain was done which revealed mycotic aneurysm of external carotid artery. The patient underwent a two-week course of a combination of intravenous antibiotics. Follow-up angiography was performed which confirmed successful treatment of mycotic aneurysm of ECA. Mycotic aneurysm of ECA is extremely rare. To our knowledge, this is the first report of mycotic aneurysm of ECA following severe TBI which was successfully treated with antimicrobial therapy.