Calf vein thrombosis corresponds to infrapopliteal deep vein thrombosis which accounts for roughly 50% of all cases of deep vein thrombosis and shares the same risk factors as proximal deep vein thrombosis. The complication rate and proper management remain debated. Recent studies suggest that the risk of proximal extension of calf vein thrombosis is 1 to 5% and that the risk of postthrombotic syndrome is 3%. In France, calf vein thrombosis is usually treated with compression stockings associated with a six week to three month regimen of anticoagulation therapy in patients presenting a transient triggering factor or longer otherwise. However, the benefit of such treatment, in terms of the hemorragic risk incurred, remains uncertain. The randomized double blind trial CACTUS (compression stocking + placebo versus compression stocking + heparin, for six weeks) that will start in September 2007, should provide answers the following question: should calf vein thrombosis be treated with anticoagulants?