We sought to determine whether there are any subgroups of patients who might benefit from endarterectomy of the asymptomatic carotid artery after successful operation for a symptomatic carotid stenosis. The incidence and outcome of stroke in the asymptomatic carotid artery distribution was prospectively studied in 966 patients who were entered into the European Carotid Surgery Trial and had a 30–99% asymptomatic carotid stenosis. The patients had been randomized to either carotid endarterectomy (61%) or no endarterectomy of their symptomatic carotid stenosis. We reviewed the literature on the risks and efficacy of carotid endarterectomy and used these data in a decision analysis. The 5-year risk of stroke lasting more than 7 days in the asymptomatic carotid distribution was 3.4%. Two independent prognostic factors were identified by means of Cox''s proportional hazards regression with stepwise forward selection: the degree of asymptomatic carotid stenosis (30–69 vs. 70–99%) and hypertension. The 5-year-restricted and quality-adjusted life expectancy for a patient with both a severe (70–99%) asymptomatic carotid stenosis and hypertension, and therefore with the highest risk of asymptomatic carotid distribution stroke, was 4.14 life years for both conservative management and for endarterectomy. Plausible changes in the estimated risk of asymptomatic carotid distribution stroke, and in the rate of complications from endarterectomy, increased the benefit of endarterectomy. But, the maximal benefit was only 0.1 quality-adjusted life years or 5 weeks, even when endarterectomy was without risk. A separate regression model, with the degree of asymptomatic carotid stenosis as a continuous variable, suggested a possible benefit of endarterectomy for the few patients (n = 27, 3%) with an 80–99% asymptomatic carotid stenosis and hypertension. Until our results are refuted in other studies, there seems to be no firm indication for operation on the asymptomatic carotid artery in patients who have been successfully operated for a symptomatic carotid stenosis, except within the context of a randomized control