The primary goal of endovascular treatment of abdominal aortic aneurysms (AAA) is prevention of death from rupture. Even in the absence of an endoleak, the AAA may continue to enlarge. The pathogenesis of this phenomenon remains unclear. Therefore, surveillance after endovascular AAA treatment must include regular evaluation of aneurysm size, or even better, aneurysm volume. Aneurysm sac enlargement without an endoleak is not a benign condition. Recurrent or persistent pressurization of the AAA sac will eventually result in rupture. Besides that, continued expansion of the AAA sac can result in dilatation of the infrarenal neck and/or iliac arteries, which may threaten the integrity of proximal and distal anastomotic seals. Many centers will take a pragmatic approach in case of endotension and a growing AAA, and convert to open surgery with removal of the endograft and placement of a regular vascular graft. Direct puncture and pharmacological intervention in the cause of sac enlargement by local instillation seems logical, but has failed so far. The third option for aneurysm sac enlargement without an endoleak is laparoscopic or open fenestration of the aneurysm. Until permanent solutions for endotension and endoleaks are found, endovascular aneurysm repair will remain an imperfect long-term treatment and continued follow-up will be mandatory.