Infectious cerebral aneurysms are uncommon, accounting for only 2.6% to 6% of all intracranial aneurysms according to autopsy studies. These aneurysms may arise from an intravascular or extravascular source of infection. The vast majority occur in the setting of bacterial endocarditis with an intravascular source of infection due to embolization of fragments of infected cardiac valve emboli. Infectious aneurysms are usually discovered after a devastating intracranial hemorrhage that carries a 60% to 90% mortality. More recently, fungal infectious aneurysms, which carry an even graver prognosis, have become more common. A high index of suspicion and early diagnosis of infectious aneurysms prior to hemorrhage is an important factor in reducing morbidity and mortality. Some lesions are effectively treated with antibiotics alone, but other require surgical intervention.