We treated six patients with post-traumatic cavernous carotid fistulae by electrothrombosis using Guglielmi's new electrolytically detachable coils. The transarterial endovascular route was chosen in five and the transvenous in one case. Exophthalmos, chemosis and/or an audible bruit disappeared immediately after therapy or in the following month in all patients suffering from these symptoms. Third and sixth cranial nerve palsies resolved in three of four patients. Clinical results were excellent in three, good in two and fair in one. In this last patient massive thrombosis of an enormously dilatated superior ophthalmic vein occurred after treatment of a giant longstanding fistula, leading to unilateral visual impairment and increased sixth nerve palsy. In our first patient the intracavernous carotid artery was occluded by balloons after coil embolisation because of improper coil position and the fear of possible thromboembolic events. Angiographic cure was demonstrated in all cases by angiograms 1-6 months after therapy. The characteristics of these new coils are easy use, manoeuvreability and retrievability. They conform ideally to the shape of the vessel lumen to be obliterated and produce practically no trauma to the vessel walls. Furthermore, they can be positioned in the sinus close to the orifice of the fistula. In the last two cases partial occlusion of the fistula was sufficient to initiate the process of complete thrombosis, and delayed, complete occlusion was observed after 1 month. In our opinion this new device is not only a major contribution to treatment of intracranial aneurysms, but may also improve the results of treatment of carotico-cavernous fistulae.