Data from autopsy studies indicate that 1% to 5% of adults have cerebral aneurysms . Most are considered to be sporadically acquired, although the risk is higher if an individual has a family history of aneurysms or autosomal dominant polycystic kidney disease . About 27,000 cerebral aneurysms rupture each year in the United States. The peak incidence is at 55 to 60 years of age, with double the number occurring in women as in men. If an aneurysm ruptures, the effect is often devastating, with a 30-day mortality rate of 45% and 30% of survivors left with moderate to severe disability .