Carotid-jugular fistulae are rare complications of penetrating head and neck trauma. We report an unusual case of an external carotid-internal jugular fistula presenting with diplopia due to sixth nerve paresis. A 38-year-old Caucasian female presented in the setting of acute neurovascular neck trauma and weeks later developed symptomatic diplopia. An acquired carotid-internal jugular fistula affecting the abducens nerve secondarily via compression from a distended inferior petrosal sinus was diagnosed and treated using endovascular coil embolisation, resolving the patient's symptoms. A posteriorly draining external carotid artery-internal jugular venous fistula can be an uncommon cause of a compressive sixth cranial nerve palsy.