Hereditary Haemorrhagic Telangiectasia (HHT) is a genetic disorder responsible for cutaneous or mucosal telangiectasia and arteriovenous malformations (AVMs). The most frequent locations are lung and brain. In contrast, orbital AVMs are very rare. We describe a case of symptomatic orbital arteriovenous malformation due to spontaneous thrombosis. A 65-year-old woman was referred for chronic right eye proptosis associated with dilation of conjunctival vessels with a jellyfish pattern. Right visual acuity was 20/40 and intraocular pressure was 40 mmHg. Personal and familial history of recurrent epistaxis, associated with multiple telangiectasia within lips and palate, led to the diagnosis of HHT. Magnetic resonance imaging (MRI) completed with cerebral angiography found a giant and occluded AVM within the right orbit. Other AVMs were also found in brain and chest, confirming the diagnosis. Antiglaucomatous eyedrops were added to reduce intraocular pressure and a steroid therapy was begun. Two months later, visual acuity decreased in the right eye, due to a central retinal vein thrombosis. In conclusion, Most brain or pulmonary AVM can be treated by embolization. By contrast, this treatment in case of orbital location can lead to central retinal artery and/or central retinal vein occlusion, which may also appear as a spontaneous complication of the orbital AVM. Therapeutic management of orbital AVM is thus not standardized, and the balance between spontaneous and iatrogenic risk of visual loss has to be taken into account.