Background: Our report summarizes and compares the characteristics of six prospective, multicenter, randomized clinical trials of carotid endarterectomy underway in North America and Europe. Summary of Review: Three trials are designed to evaluate the safety and efficacy of endarterectomy in patients with asymptomatic carotid artery stenosis. The other three trials enroll patients who have had transient ischemic attacks or a minor cerebral infarction in the distribution of the randomized artery. Considered together, these six clinical trials span the range of candidates for carotid endarterectomy. The inclusion and exclusion criteria, methodology, and statistical considerations of each study are detailed in tables. Conclusions: The results from these trials will be helpful in resolving some of the questions surrounding endarterectomy, provided the similarities and differences in the study designs are considered when interpreting the results. © 1992 American Heart Association, Inc.