A multicenter phase II clinical trial of aneurysm treatment was performed with the modified Gore Excluder bifurcated endoprosthesis (m-EBE, n = 193) and compared with previously reported results from the same group of the original unmodified device (EBE, n = 253) or standard open aneurysm exclusion (control, n = 99). Graft modifications were primarily related to the proximal attachment site and included an increase in the length of the external expanded polytetrafluoroethylene and modifications of the anchor configuration. Preprocedural characteristics, periprocedural clinical events, and postprocedural clinical and radiographic follow-up at 1, 6, 12, and 24 months were analyzed with univariate and multivariate statistics. Device placement was successful in all cases, and there were no aneurysm ruptures in any group. Survival to 2 years was similar in all groups. Early major adverse events with the m-EBE were similar to those with the EBE (14.5% vs. 14%, P = 0.9) and markedly reduced compared to the control group (60.6%, P < 0.0001). After 30 days, there was no significant difference in the occurrence of major adverse events between endoluminal treatment and open controls. The rates of documented endoleak and increased aneurysm size at each follow-up interval were not significantly different between the two endoluminal devices. However, there was a trend toward fewer reinterventions from 14 to 28 months with the m-EBE (2% vs. 6% with the EBE, P < 0.06). There were also significantly fewer major adverse events associated with the m-EBE compared to the EBE during 14- to 28-month follow-up (15.6% vs. 24.9%, P = 0.037), in part due to the difference in reinterventions. The safety and efficacy of the m-EBE are statistically similar to the original device, although there was a reduction in major late adverse events between the two iterations of the endograft. This difference appears to be related to increased operator experience and changing treatment algorithms. Compared with open aneurysm repair, endoluminal repair with the m-EBE offers advantages in the reduction of early major adverse events while maintaining similar survival and rupture-free outcomes in the intermediate term.