The most common (80%) cause of non-traumatic subarachnoid hemorrhage (SAH) = ruptured saccular (berry) aneurysm.
Saccular aneuryms are thought to be present in up to 5% of the population.
There is a strong familial association with cerebral aneurysms, and prevalence is increased in people with Marfan Syndrome and Polycystic Kidney Disease.
Other causes of non-traumatic SAH include: AV malformation, cavernous angioma, mycotic aneurysm, and blood dyscrasia.
