This study reviewed a large national core laboratory database for the Ancure (Guidant, Menlo Park, California) phase I and II trial of overall aneurysm sac regression after endovascular aneurysm repair. Data were reviewed for aneurysm size and endoleak in follow-up. Endoleak was recorded as well as maximum major and minor axis aortic diameters. Included were patients with baseline assessment within 3 months of implantation and at least 24 months of follow-up, and 444 were available for review. The mean baseline aortic diameter was 56.6 mm; mean follow-up was 48.7 months. Of these patients, 129 (29.5%) had aneurysm regression to less than 40 mm, 42 (9.5%) regressed to less than 35 mm, and 12 (2.7%) had complete aneurysm sac obliteration. Multivariate analysis demonstrated that baseline aneurysm size was the only predictor of aneurysm size regression. Significant sac regression is common after Ancure aneurysm repair and appears to be related primarily to initial aneurysm size.