Dacron prostheses are the most widely used grafts in replacement procedures for abdominal aortic aneurysms, having been proven as the most reliable substitute for arterial replacement. However, we present herein the rare case of an 82-year-old woman in whom nonanastomotic aneurysm formation occurred in the graft as a complication associated with a Dacron prosthesis. The patient presented with a pulsatile mass in the right inguinal region. She had undergone surgery 13 years earlier for an abdominal aortic aneurysm, at which time an aortobifemoral graft reconstruction had been performed with a double-velour knitted Dacron prosthesis. The pulsatile mass was found to be a nonanastomotic aneurysm of the right limb of the bifurcated graft with an intact distal anastomosis. In this case, the development of the graft aneurysm seemed to result from deterioration of the Dacron prosthesis itself due to mechanical fatigue caused by the inguinal band.