Cockett's syndrome is due to compression of the left common iliac vein by the left iliac artery. Anatomical factors and venous anomalies contribute to the venous obstruction. Clinical symptoms only develop in cases with marked compression; they consist of functional disorders predominant in the left lower limb and, frequently, recurrent oedema. The compression may be revealed by complications such as deep thrombosis of the iliac vein or veins of the calf, or pulmonary embolism. The diagnosis is made by phlebo-ilio-cavography.