Trauma can lead to stroke by causing a cervical or cerebral arterial dissection: a tear in the wall of an artery with dissection of blood through its layers which can be a nidus for thrombus formation and artery-to-artery embolic events.  Although trauma is extraordinarily common—there are 28 million emergency department visits for trauma in the U.S. every year—and arterial dissection is a common cause of stroke in the young, there are no proven methods of primary stroke prevention in this setting, for either children or adults.  Data on the incidence, timing, and predictors of stroke after trauma are lacking.  Funded by the American Heart Association, PSAT is a retrospective cohort study of children and young adults exposed to trauma, set within Kaiser Permanente Northern California, a large integrated health care plan.   The specific aims of this study are: (1) to estimate incidence of ischemic stroke within a cohort of children and young adults seeking emergency medical care for trauma, and establish the time window of greatest risk; (2) to identify predictors of short-term stroke risk after trauma; (3) to design a large multicenter prospective study to develop a stroke prognostic score for victims of trauma, and perform a single-center feasibility study of prospective data collection.  The long-term goal of this research is to develop an approach to stroke prevention after trauma that is safe, easily implemented, and cost-effective.