This study reports the incidence and sequelae of migration of the Nellix (Endologix Inc, Irvine, Calif) endoprosthesis after endovascular aneurysm sealing.A review was performed of the follow-up imaging of all endovascular aneurysm sealing patients in a university hospital endovascular program who had a minimum follow-up of 1 year. The first postoperative and latest follow-up computed tomography scans were used to measure the distances between the proximal and distal borders of the stent grafts relative to reference vessels using a previously validated technique. Device migration was based on previously established criteria and defined as any stent graft movement of ≥4 mm related to a predefined reference vessel. Device movement in a caudal direction was given a positive value, and movement in a cranial direction was denoted by a negative value.Eighteen patients (35 stent grafts) were eligible for inclusion in this retrospective review. The mean preoperative abdominal aortic aneurysm diameter was 57 mm (standard deviation [SD], 5; range, 50-67 mm) and aortic neck length was 30 mm (SD, 16; range, 6-62 mm). Proximal migration, according to study definitions, was identified in six stent grafts (17%), all in a caudal direction. At 1 year the mean proximal migration distance was +6.6 mm (SD, 1.6; range, +4.7-+9.2 mm). Migration occurred in a single stent graft in four patients and bilaterally in one. No distal migration occurred.Proximal migration of the Nellix endoprosthesis does occur and was without any sequelae in our series. Further investigations into the long-term positional stability of the Nellix device, together with a more thorough understanding of the etiology and consequences of migration, are required.