Scientific evidence suggests that a genetic component plays an important role in the development of intracranial aneurysms, however the specific genes have not been identified. The Familial Intracranial Aneurysm Study is a collaborative research effort of neurologists and neurosurgeons throughout the United States, Canada, Australia and New Zealand to identify possible genes that may increase the risk of stroke, and particularly, the development of aneurysms in the blood vessels of the brain. This study will involve 475 families with multiple affected family members, and will also determine the effect of environmental factors such as cigarette smoking and high blood pressure on the expression of the genes.A group of physicians from throughout North America, Australia and New Zealand have formed a collaborative effect to identify genes that may be important in the development of aneurysms in the blood vessels of the brain. This study of affected individuals and families, known as the Familial Intracranial Aneurysm (FIA) study, is sponsored by the National Institutes of Health and has involved over 475 families.