Genetics contribute to all aspects of cerebrovascular disease from the underlying pathology, through acute neuronal injury, to recovery and long-term prognosis. By understanding better the genetic contribution to the risk for cerebrovascular disease we can work toward the day when simple genetic tests can be used to assess an individual's risk for stroke (and cardiovascular disease) in the same way that we now use routine screening of blood pressure or cholesterol (Harrap, 1994b). Finally, it is worth noting that genetic effects do not work 'in vacuo'. They are subject to environmental influences which impact on the individual's phenotypic characteristics. Modification of these environmental factors may have a significant effect on the action of certain expressed genes and their putative mutations.