A 41-year-old man with visual loss due to bilateral compressive optic neuropathy resulting from severe ophthalmic Graves' disease was found on presentation to have 'blow-out' fractures of both orbital floors. Five months earlier he had been involved in a minor road traffic accident and sustained a right orbital floor fracture. The greatly enlarged extraocular muscles and associated high intraorbital pressure resulted in a spontaneous left orbital floor fracture-an auto-orbital decompression. His right orbital floor fracture may also have occurred spontaneously prior to his accident or perhaps the floor was already sufficiently weakened that even minor trauma led to a fracture. Although auto-orbital decompression may have delayed the onset of visual loss it was not effective in relieving optic nerve compression, and systemic steroid therapy was required to improve vision.