A male smoker in his 60s with hypertension and hyperlipidaemia presented with progressive swelling of his left leg, abdominal discomfort and oliguria. He was obese and had an extensive left deep vein thrombosis (DVT) clinically. Blood tests revealed acute renal failure, and the clinical suspicion was of a urological malignancy causing an obstructive nephropathy and DVT. A CT scan showed a large (9.5×9.8 cm) infra-renal abdominal aortic aneurysm, which had a fistulous connection to the left common iliac vein (fig 1). Retrograde filling of the venous system and obstruction to venous return led to engorgement of the left leg, mimicking a DVT (fig 2). The renal arteries were patent, but contrast was also seen filling the renal veins with no cortical renal enhancement, suggesting retrograde high-pressure flow, with obstruction to venous return and consequent venous infarction, as a mechanism for acute renal failure. The patient rapidly deteriorated, developed multiorgan failure, and died before emergency surgery.