This is a multi-investigator study based on the pathophysiology of carotid atherosclerosis and the variables that cause certain plaques to become symptomatic.Patients enrolled in this study will be those patients undergoing a carotid endarterectomy. This will include both symptomatic and asymptomatic patients, and there are a variety of atherosclerotic risk factors representing this patient population.Patients may or may not have had strokes or transient ischemic attacks (TIAs).Pre-operatively patients will be reviewed for their medical history and atherosclerotic risk factors. Plaque removed during routine carotid endarterectomy will be examined for study purposes.