Unruptured intracranial aneurysms occur in up to 6 percent of the general population. Most persons with these aneurysms remain asymptomatic and are usually unaware of their presence. Risk factors for the formation of aneurysms include a family history of aneurysm, various inherited disorders, age greater than 50 years, female gender, current cigarette smoking, and cocaine use. Because of the morbidity and mortality associated with surgical intervention, screening for aneurysms remains controversial. Two groups of patients may benefit from early detection: those with autosomal dominant polycystic kidney disease and those with a history of aneurysmal subarachnoid hemorrhage. These patients should undergo magnetic resonance angiography, followed by neurosurgical referral if an aneurysm is detected. Screening of patients who have two or more family members with intracranial aneurysms is controversial. Screening of patients who have one first-degree relative with an aneurysm does not appear to be beneficial.