We report, with serial angiograms, a case worsening of dural arteriovenous fistulae (DAVFs) located at the hypoplastic right cavernous sinus and draining into the left superior ophthalmic vein across the inter-cavernous sinus. The patient presented with sudden onset of external ophthalmoplegia and deterioration of visual acuity on the left. An imaging work-up at the day of admission included contrast-enhanced computed tomography and conventional catheter angiography, which demonstrated complete thrombosis of the left cavernous sinus. There was no strong evidence to suggest DAVFs other than small faint opacification of the posterior cavernous sinus on the right at the late arterial phase. For this reason a diagnosis of left cavernous sinus thrombosis was made, followed by aggressive anticoagulation therapy with intravenous administration of antibiotics. Although the patient's eye symptoms improved significantly after the anticoagulation therapy, the follow-up angiogram obtained 5 days after admission demonstrated small right cavernous sinus DAVFs, which drained into the left superior ophthalmic vein. The patient was followed up conservatively at the out-patient clinic. Three-month follow up angiograms demonstrated spontaneous cure of the DAVF. Also noted was a complete recovery of external ophthalmoplegia with significant improvement of left visual acuity. The alternation of clinical and angiographic findings in this case may help to understand the etiology of paradoxical worsening of cavernous sinus DAVF. In selected cases, anticoagulation therapy may help to improve the prognosis of paradoxical worsening.