Objective: The factors associated with access site failure after ultrasound-guided percutaneous access for aortic endograft procedures remain poorly characterized. We developed a prediction model to risk stratify patients for access site failure.Methods: We performed a retrospective institutional review of consecutive patients who underwent endovascular aneurysm repair (EVAR), fenestrated EVAR (FEVAR), or thoracic endovascular aortic repair (TEVAR) from 2014 to 2016. We excluded patients undergoing direct aortic access through sternotomy and patients treated with physician-modified endografts, given reporting restrictions. Our primary outcome was groin access site failure, which included bleeding and thrombosis. An 8-point risk model was created for access site failure using multivariable fractional polynomials and internally validated using bootstrapping.Results: We identified 469 femoral arteries from 247 patients undergoing endovascular aortic repair procedures (EVAR, 75%; FEVAR, 8.0%; TEVAR, 17%). Surgeons performed percutaneous access in 97.2% of the femoral arteries, with 99.6% ultrasound use. Twenty-seven (5.9%) access site failures occurred (17 bleeding, 10 thrombosis), all treated with groin cutdown, for a successful percutaneous femoral artery access rate of 94%. Of the 215 patients with attempted bilateral percutaneous access, 90% had successful bilateral access. However, FEVAR had lower rates of successful bilateral access (FEVAR, 78%; EVAR, 91%; TEVAR, 94%; P = .03). Factors independently associated with percutaneous access site failure were femoral artery outer wall diameter (per millimeter increase: odds ratio [OR], 0.003 [0.0002-0.1]; P < .001), femoral artery stenosis >50% (OR, 22.3 [2.7-183.2]; P < .01), and urgent/emergent intervention (OR, 3.6 [1.2-11.0]; P = .03). A risk prediction model based on these criteria produced a C statistic of 0.89, a Hosmer-Lemeshow goodness of fit of 0.99, and a Brier score of 0.04. Excluding treatment for ruptured aneurysms, cutdown for access failure and planned initial groin cutdown resulted in longer postoperative lengths of stay and higher rates of access-related readmission, return to operating room, groin infection, and myocardial infarction compared with successful percutaneous access. There was no difference in major adverse events between planned initial groin cutdown and cutdown after failure; however, the small number of patients in these two comparison groups limits the statistical power to detect a difference.Conclusions: Percutaneous ultrasound-guided access can be safely performed in almost all patients undergoing endovascular aortic procedures, but access site failures do occur. This risk score can help users select patients with high likelihood of success, identify patients who need close scrutiny with postclosure femoral duplex ultrasound, and provide patient guidance about risk of unplanned groin cutdown.