Tumors caused by augmentation in volume of normal vessels or by formation of new vessels occur in the orbit as angiomas of various types, or varicosities, with or without direct arterial communication. Should such tumors become pulsatile because of copious arterial supply or because of juxtaposition to a large artery, they tend to become larger through expansion of existing blood spaces and involvement of contiguous tissue. The bony walls of the orbit may be eroded by the pulsating soft tissue, and bony foramina may become greatly enlarged by pulsating, dilated vessels. Exophthalmos is the most frequently observed sign of the presence of any orbital tumor, but in the group of vascular tumors it takes on particular significance. Pulsating exophthalmos is usually rapidly progressive and may require ligation of one or more of the carotid arteries. Not all pulsating exophthalmos is due to aneurysm of the cavernous sinus or to