The study of carotid artery occlusive disease interventions can be divided clinically into the treatment of asymptomatic and symptomatic diseases. Clinical trials that have studied or are currently studying asymptomatic disease include: the Carotid Artery Stenosis with Asymptomatic Narrowing Operation Versus Aspirin study; the Mayo Asymptomatic Carotid Endarterectomy trial; Veterans Administration Cooperative Trial on Asymptomatic Carotid Stenosis; and the Asymptomatic Carotid Atherosclerosis Study. Trials for the treatment of symptomatic disease include: the North American Symptomatic Carotid Endarterectomy Trial; the European Carotid Surgery Trial; and the Veterans Administration Cooperative Study. In the earliest trials conducted to study asymptomatic disease medical therapy was slightly favored; on close scrutiny these studies were flawed and the findings appeared to be equivocal. The more scientific and appropriate trial, which was ended due to ethical concerns, revealed a clear advantage in patients who underwent surgery for greater than 60% stenosis and when the surgical center demonstrated less than 3% surgical risks. All trials studying symptomatic disease found a significant decrease in subsequent stroke when surgical intervention was performed. It is now judged that patients with greater than 50% stenosis receive significant benefit. In this paper the authors review the data from all of these studies. They also review data for special circumstances, such as critical stenosis and patients with symptomatic and asymptomatic Hollenhorst plaques. It is their opinion that these data have allowed surgeons to make much more educated decisions when considering the treatment of patients with carotid artery occlusive disease.