Objectives: We sought to examine the nature of fungal balls of the sphenoid sinus, in particular the exposure of adjacent skull base structures and the potential for surgical morbidity. Methods: We retrospectively reviewed our series of 17 cases of sphenoid sinus fungal balls seen between 1998 and 2005 with reference to their diagnosis, radiologic changes, histopathology, and surgical management. Results: Exposed structures included the pituitary fossa, cavernous sinus, and cavernous internal carotid artery, but this exposure did not result in an increase in perioperative complications. Sclerotic thickening of the sinus walls persisted, probably representing a chronic osteitis in response to concurrent bacterial infection. This appeared to be protective against further sinus wall erosions. Wall erosions did not heal. One patient demonstrated what appeared to be invasive fungal disease from a fungal ball. Conclusions: Sphenoid sinus fungal balls can occur with minimal symptoms in a mainly elderly population and require surgical removal. Sphenoid sinus fungal balls have a low rate of operative morbidity and should be effectively managed by transnasal endoscopic sphenoidotomy alone.