OBJECTIVE: This is a natural history/disease pathogenesis protocol for evaluation of patients with or at risk for acute stroke, transient ischemic attack (TIA), or other disturbances of cerebrovascular circulation. The purpose of this protocol is to generate natural history data to serve as the basis for future hypothesis-driven protocols as well as to contribute to the clinical and physiological understanding of cerebrovascular disease through the description of disease manifestations and the relationship among clinical, hematologic, and radiologic variables, as well as identifying potential subjects for future studies on stroke and other cerebrovascular diseases.