Identifying patients at risk for aneurysm rupture and sac expansion after open and endovascular abdominal aortic aneurysm (AAA) repair (EVAR) may help to attenuate this risk by intensifying follow-up and early detection of problems. The goal of this study was to validate the St George's Vascular Institute (SGVI) score to identify patients at risk for a secondary intervention after elective aneurysm repair.A post hoc on-treatment analysis of a randomized trial comparing open AAA repair and EVAR was performed. In this multicenter trial, 351 patients were randomly assigned to undergo open AAA repair or EVAR. Information on survival and reinterventions was available for all patients at 5?years postoperatively, for 79% at 6?years, and for 53% at 7?years. Open repair was completed in 173 patients and EVAR in 171, based on an on-treatment analysis. Because 17 patients had incomplete anatomic data, 327 patients (157 open repair and 170 EVAR) were available for analysis. During 6?years of follow-up, 78 patients underwent at least one reintervention. The SGVI score, which is calculated from preoperative AAA morphology using aneurysm and iliac diameter, predictively dichotomized patients into groups at high-risk or low-risk for a secondary intervention. The observed freedom from reintervention was compared between groups at predicted high-risk and predicted low-risk.The 20 patients in the high-risk group were indeed at higher risk for a secondary intervention compared with the 307 patients predicted to be at low risk (hazard ratio [HR], 3.82; 95% confidence interval [CI], 2.05-7.11; P?<.001). Discrimination between high-risk and low-risk groups was valid for EVAR (HR, 4.06; 95% CI, 1.93-8.51; P?<.001) and for open repair (HR, 3.41; 95% CI, 1.02-11.4; P?= .033).The SGVI score appears to be a useful tool to predict reintervention risk in patients after open repair and EVAR. Society for Vascular Surgery.