Routine ultrasonographic screening and examination of patients with and without specific symptoms of carotid artery disease now provides greater understanding of the natural history of the disease. In one year, 194 ulcers were detected, classified, and followed. No initially asymptomatic ulcer shallower than 2 mm later became asymptomatic, and it is concluded that a trial of antiplatelet therapy in these patients would be inconclusive. More than a third of the initially asymptomatic ulcers from 2 to less than 4 mm in depth gave rise to lateralizing symptoms that required surgery, The effects of antiplatelet therapy in this vulnerable population could be readily followed by ultrasonographic monitoring. All patients with ulcers 4 mm or more in depth were initially symptomatic and so required surgery.