Background: Many patients with an abdominal aortic aneurysm (AAA) who are cared for by internists are not good candidates for surgery. Elective repair is usually deferred in these patients until the AAA reaches a diameter at which the estimated risk of rupture is believed to outweigh the operative risk. The risk of rupture is usually estimated by a consulting vascular surgeon, but whether these estimates are well-supported or consistent has not previously been assessed. Objective: To determine the agreement among vascular surgeons about the risk of rupture of large AAAs. Methods: All individual members of the Society for Vascular Surgery (Manchester, Mass) residing in the United States were mailed a survey asking for their estimates of the likelihood of rupture of large AAAs. Results: The response rate was 66% and the 257 respondents who reported that they were practicing vascular surgeons constitute the study group. The median estimates of the 1-year risk of rupture were 20% for 6.5-cm AAAs and 30% for 7.5-cm AAAs, with one third of respondents estimating 50% or greater risk of rupture for 7.5-cm AAAs and nearly one third estimating 30% or greater risk of rupture for 6.5-cm AAAs. The responses spanned a wide range and were generally much higher than would be expected based on published data and estimates. Conclusions: This survey demonstrates profound disagreement among vascular surgeons about the risk of rupture of large AAAs, reflecting a lack of pertinent published data. Better data are necessary and are being collected.