BACKGROUND AND IMPORTANCE: Endovascular treatment of giant carotid cavernous aneurysms (GCCAs) may be associated with complications including rapid intrasaccular thrombosis, embolic ischemic stroke, and caroticocavernous fistula. CLINICAL PRESENTATION: A female in her 6th decade presented with a chronic, right partial abducens nerve palsy. Magnetic resononance angiography demonstrated a 25-mm right GCCA causing mass effect on the right cavernous sinus. Coil embolization of the aneurysm and parent vessel was performed after passing a balloon test occlusion. Final angiography demonstrated complete embolization of the aneurysm, however, absent ipsilateral cavernous sinus drainage, which was present previously. Intraprocedurally, the patient had ipsilateral proptosis and chemosis. Once extubated, urgent ophthalmology review documented preserved and symmetrical visual acuity with both pupils reactive to light. Intraocular pressure was 19-mm and 11-mm Hg in the right and left eye, respectively. The right eye had -2 abduction with otherwise intact extraocular movements. Acute management included a total of 16-mg IV dexamethasone on day 1, followed by a course of oral steroids and prophylactic low molecular weight heparin. Postprocedure computed tomography of the head demonstrated periorbital soft tissue edema and dilatation of the right superior ophthalmic vein, which peaked at 6 hours postprocedure. The patients' ocular findings and visual disturbances subsided within 36 hours postprocedure. The chronic partial abducens nerve palsy remained. CONCLUSION: Acute proptosis, chemosis, and visual disturbances may occur from mass effect on the cavernous sinus with venous outflow obstruction after GCCA embolization. This is thought to be secondary to increased mass effect from intrasaccular thrombosis and the large coil mass.