A carotid cavernous fistula is an abnormal communication between a branch of the carotid artery and the cavernous sinus generating an arteriovenous fistula that can cause severe ocular damage. We hereby report two cases of carotid cavernous fistulas. A 69-year-old male with a 2-month history of right eyelid swelling and red eye aggravated by diplopia, exophthalmus, and limitation of ocular movements one week before consulting. On admisson his visual acuity in the right eye was good (0.5) and biomicroscopy showed arterialization of conjunctival vessels. An orbital CAT scan showed a dilatation of the superior orbital vein characteristic of carotid cavernous fistula. A balloon tamponade of the fistula was performed too late (after 3 weeks) and the eye went blind. A 39-year-old female consulted for an acute proptosis of the right eye and severe visual loss. Biomicroscopy showed arterialization of the conjunctival vessels and the CAT scan disclosed a dilatation of the superior orbital vein. She was immediately subjected to a neuroradiological fistula closure with recovery of visual acuity to 1.0 (20/20). Our main purpose is to emphasize the importance of the opportune diagnosis and treatment of these fistulas to prevent visual loss and eventual blindness, as occurred in our first patient (Rev Méd Chile 2004; 132: 1221-6)