Embolisation of a carotid cavernous fistula by means of a detachable balloon is a well-established method for treating carotid cavernous fistulas while preserving a patent internal carotid artery. However, failure to embolise the carotid cavernous fistula may occur. Herein we describe a stent-assisted Guglielmi detachable coil embolisation that completely occludes the fistulous opening rather than fills the cavernous sinus. By applying this technique, we successfully treated a carotid cavernous fistula, without compromise of the parent internal carotid artery when the balloon technique failed.