The advent of non-invasive methods of imaging intracranial blood vessels has facilitated screening for intracranial aneurysms in people who are at risk. A strong risk factor for intracranial aneurysm, which causes subarachnoid haemorrhage, is a positive family history, defined as two or more first-degree relatives with subarachnoid haemorrhages (relative risk [RR]=6.6). The greatest familial risk is associated with an affected sibling. Another strong risk factor is polycystic kidney disease (RR=4.4). People who have these risk factors are potential candidates for screening. Even if screening does not find abnormality, there is a high risk of new aneurysms 5 years later. Repeated screening might be done, although the optimum interval between screening assessments and the duration of repeated screening is unclear. Patients who have survived a subarachnoid haemorrhage are at increased risk of another from a newly developed aneurysm, but whether screening is beneficial in such patients is not clear. Most occurrences of subarachnoid haemorrhage in the general population are related to the more common risk factors of hypertension (RR=2.8) and smoking (RR=1.9). Therefore, screening of individuals who have a family history of subarachnoid haemorrhage or polycystic kidney disease will have little effect on the incidence of subarachnoid haemorrhage in the general population. When patients present for screening, the construction of a family tree and discussion of the history of relatives with stroke can be revealing. Before referring a patient for non-invasive imaging of the circle of Willis, the physician should discuss the risks and benefits of screening, the implications for holding a licence to drive or fly and for life insurance, and whether or not the patient wants to be informed about other incidental findings.