We report a case of unruptured fungal internal carotid artery (ICA) aneurysm and review the pertinent literature. A 79-year-old man presented with decreased visual acuity on the right side, and he was diagnosed with retrobulbar optic neuritis. Medical treatment with steroids resulted in Aspergillus meningoencephalitis spreading to the bottom of bilateral frontal lobes, caused by an intracranial extension of sphenoid sinusitis. Magnetic resonance imaging (MRI) performed 26 days after the start of antifungal therapy showed a denovo right ICA aneurysm projecting anteriorly into the sphenoid sinus. As the aneurysm grew rapidly, it was trapped surgically after establishing a high-flow bypass from the external carotid artery to the middle cerebral artery. The patient's postoperative course was uneventful. Anti-fungal medication was continued until plasma concentrations of beta-D-glucan decreased to within normal limits. Although fungal ICA aneurysm carries a high mortality rate, early detection and prompt treatment by trapping and high-flow bypass can lead to good clinical outcome.