['Renal insufficiency (RI) seems to be a source of complications after carotid endarterectomy (CEA). However, published studies do not use a common definition of RI. Our objective was to analyze the effects of RI on carotid surgery using three classifications of renal function.', 'Using a prospective database, we studied renal function and postoperative complications in patients operated on between January 1, 2003 and December 31, 2008. Renal function was studied using the level of plasma creatinine, creatinine clearance calculated according to the Cockcroft formula, and to the Modification of Diet in Renal Disease (MDRD) equation. For each method, the patients were divided into three groups: normal renal function, moderate RI, and severe RI. The principal judgment criterion was the 30-day non-fatal stroke and death rate.', 'The analysis concerned 961 CEAs carried out in 901 patients. The 30-day non-fatal stroke and death rate was 2%. In the analysis of renal function using the level of creatinine, there was no statistical difference between the groups in the 30-day stroke and death rate (normal renal function: 1.8%, moderate: 2.7%, severe: 8.3%, P = .21). The analysis of renal function according to creatinine clearance calculated using the Cockcroft formula showed that in the severe RI group, the stroke and death rate was higher than in the other two groups (normal renal function: 1.7%, moderate RI: 1.4%, severe RI: 7.5%, P = .004). Analysis using the MDRD formula showed similar differences between the severe RI group and the other two with a higher rate of 30-day stroke and death (normal renal function: 1.4%, moderate RI: 1.7%, severe RI: 12.5%, P < .001). Subgroup analysis showed that among patients with severe RI according to the creatinine clearance, those with symptomatic carotid stenosis had the highest incidences of non-fatal stroke and death (Cockcroft, n = 19: 21.1%, MDRD, n = 10: 40%).'] Is the impact of renal insufficiency on the outcome of carotid surgery influenced by the definition used?