What causes a brain aneurysm? Brain aneurysms can happen to anyone at any age, but are most common in adults between the ages of 30 and 60, as well as women, and in those with certain inherited disorders. According to the Brain Aneurysm Foundation Brain aneurysms are also not rare—one in every 50 people, or about 6.5 million people in the US have an unruptured brain aneurysm. How is a brain aneurysm treated? Treatment for a brain aneurysm depends on the type, size, and location of the aneurysm, risk of rupture, the person's age and health, personal and family medical history, and risk of treatment.