Inflammatory abdominal aortic aneurysm masquerading as occlusion of the inferior vena cava. Inflammatory aneurysms are an uncommon disorder that represent between 5% and 10% of abdominal aortic aneurysms. Their presentation is often variable and may include pain and obstruction of adjacent anatomic structures. This report describes a 68-year-old man who sought treatment after insidious onset of progressive bilateral lower extremity edema over a 6-month period. Noninvasive studies were suggestive of bilateral iliac vein occlusion, and a venogram showed a nearly obstructed vena cava from external compression. A CT scan showed a thick-walled infrarenal abdominal aneurysm. At exploration an inflammatory abdominal aortic aneurysm was found. Because of the presence of dense inflammatory changes surrounding the aneurysm and extending into the pelvis, the surgical procedure of choice was an aortobifemoral bypass graft done with Dacron. The aneurysmal wall was debrided from the vena cava. His postoperative course was uneventful, his edema resolved, and follow-up noninvasive studies were normal. Postoperative venography showed resolution of the extrinsic compression of the vena cava. 