Mycotic aneurysms of the extracranial carotid arteries are rare, with only 27 cases reported in the English literature. The causative organism is most frequently Staphylococcus but infections due to Streptococcus, Salmonella and Klebsiella have been reported. Escherichia coli has been reported as the causative organism in three cases. Mycotic aneurysms usually present in the setting of generalized sepsis such as postoperative infection, septicaemia, dental sepsis, drug addiction or bacterial endocarditis. We report a patient who presented with a mycotic aneurysm of the internal carotid artery 2 months after undergoing a laparotomy for perineal sepsis.