The purpose of this case report is to familiarize the sinus surgeon with the possibility of the rapid development of internal carotid artery aneuryams from fungal infections of the sphenoid sinuses. A renal dialysis patient with progressive loss of vision was treated with high doses of steroids for the presumed diagnosis of temporal arteritis. Subsequent work-up included a magnetic resonance arteriogram (MRA) and computed tomography (CT) with contrast that failed to demonstrate aneurysmal changes of the carotid arteries but suggested the presence of a mycotic infection of the sphenoid sinuses. During a sphenoidotomy two days later, in addition to the anticipated aspergillus infection of the sinuses, an aneurysm extending from the left internal carotid artery into the sphenoid sinus was encountered. An emergency arteriogram immediately following the surgery revealed a second newly developed large mycotic aneurysm of the right internal carotid artery filling the right sphenoid sinus as well. This case report documents the rapidity with which mycotic aneurysms can develop from a sphenoid sinus infection secondary to aspergillosis in an immunocompromised host.