There has been a noted increase in the incidence of intracranial aspergillosis; this is often attributed to the wider use of antibiotics, corticosteroids, and immunosuppressants. Fungal cerebral aneurysms due to aspergillosis after neurosurgery remain extremely rare; in fact, only seven cases have been reported in the literature. In this study, we present a patient with an Aspergillus aneurysm that elicited subarachnoid hemorrhage after endoscopic endonasal surgery (EES) for craniopharyngioma. A 70-year-old woman with recurrent craniopharyngioma and steroid treatment underwent uneventful EES. On the 5th postoperative day, she suffered subarachnoid hemorrhage. As per her computed tomography angiography findings, an aneurysm was detected on the left internal carotid artery (ICA). Subsequent digital subtraction angiography showed occlusion of the ICA and an irregularly shaped wall. The diagnosis was pseudoaneurysm. We then performed craniotomy to place a left high-flow bypass and to trap the pseudoaneurysm. Despite continuous intensive care, she died on the 25th postoperative day of a huge, left cerebral infarct. The final diagnosis was made at autopsy; it revealed destruction of the ICA and Aspergillus invasion of the vessel wall, confirming the presence of a true fungal aneurysm. Perioperatively, patients with potential immunosuppression must be carefully managed. Advanced age is a risk factor. As surgery via the paranasal sinuses raises the risk for aspergillosis, fungal infection must be ruled out in patients whose postoperative course is deemed concerning.