Data on the prevalence of intracranial aneurysms in the general population come from autopsy and from angiography series. A recent review found that the prevalence of intracranial aneurysms for adults without a history of subarachnoid hemorrhage (SAH) is approximately 2%, with a male to female ratio of approximately 1 to 1.3. The same analysis found that the prevalence of aneurysms increases with age, peaking in the 69–79 year age group. Nearly half of all intracranial aneurysms become symptomatic during the patient's lifetime, usually presenting as subarachnoid hemorrhage. In North America, approximately 28,000 cases of aneurysmal SAH occur each year, mostly in adults.

As opposed to fusiform aneurysms, which are encountered in the extracranial peripheral vasculature, intracranial aneurysms are typically saccular in morphology. Intracranial aneurysms possess a well-defined neck and sac distinct from the lumen of the parent vessel and are frequently located at proximal intracranial arterial branching points. Although the pathophysiology of intracranial aneurysms is controversial, they are thought to arise from defects (congenital or acquired) in the muscularis media. Once an aneurysm has developed, conditions such as hypertension and tobacco smoking will likely increase the risk of rupture, leading to SAH. Certain conditions (e.g., autosomal dominant polycystic kidney disease, Ehlers-Danlos syndrome type IV, Alpha-1 Antitrypsin Deficiency (A-1ATD)) are associated with the formation of cerebral aneurysms, presumably from the predisposition for the development of focal weak spots in vessel walls near arterial branch points.