So-called direct carotid-cavernous fistulas (CCFs) are commonly treated by detachable balloons or coils to occlude the shunt while sparing the carotid artery. Liquid embolic agents have been rarely used, and in particular, to the authors' knowledge, the use of Onyx as the sole agent has never been reported in an indexed publication.The authors describe a case series of 5 patients with posttraumatic CCF in whom embolization with Onyx was prospectively used as the sole strategy of management.Complete occlusion was obtained at the end of the procedure in 4 cases, and the lesion in the remaining patient subsequently occluded at the 6-month follow-up evaluation.As endovascular techniques for treatment of direct CCFs continue to evolve, this novel approach with Onyx as the sole embolic material seems promising in treating these lesions.