Angiographic and/or operative follow up studies on 19 patients with angiographically demonstrated subtotal carotid artery stenosis showed the following results: In 3 out of 16 cases where no immediate operation of the stenosis was performed, complete occlusion followed within a week of the angiographic demonstration of the stenosis. Though intramural artifacts did not occur, this could be a consequence of the angiographic procedure (temporary fall of blood pressure?). In 4 out of 7 cases with subtotal stenosis where the diagnosis was known for at least 6 months, no occlusion occurred. The blood flow through a subtotal carotid artery stenosis might not be as small as is usually assumed, as illustrated by 2 out of 3 cases where a definite increase in the symptoms occurred on complete occlusion of the the vessel. The results indicate that cases of subtotal stenosis should be promptly treated by disobliteration.