We performed a national cross-sectional and prospective large epidemiological cohort study in patients with ST. Office- and hospital-based vascular medicine French practitioners enrolled all consecutive patients with a symptomatic ST of the lower limbs at least 5 cm long documented by compression ultrasonography. Follow-up was three months. All events were adjudicated by a central committee.

Between March 2005 and October 2006, 844 patients (median age [range]: 65 [18-98] years; 547 women) were included. At inclusion, confirmed deep-vein thrombosis and/or symptomatic pulmonary embolism was associated with ST in 24.9% (n=210) of patients. Among the 600 patients with isolated ST (i.e. without deep-vein thrombosis or pulmonary embolism at inclusion), 10.4% (n=56) developed venous thromboembolic complications at three months, including the following symptomatic events: pulmonary embolism (0.4%, n=2), deep-vein thrombosis (2.8%, n=15), extension of ST (3.1%, n=17) and recurrence of ST (1.9%, n=10). These complications occurred despite the use of various anticoagulant strategies in 90.5% (n=540) of patients; four independent risk factors increased the risk of these complications: male sex, cardiac or respiratory insufficiency, history of deep-vein thrombosis or pulmonary embolism and no history of varicose veins.

Inclusion Criteria:

• all consecutive patients aged 18 years or over, with a symptomatic ST of the lower limbs at least 5 cm long on compression ultrasonography.

Exclusion Criteria:

• patients who had undergone surgery under general or loco-regional anaesthesia in the previous 10 days, those in whom ST had occurred after sclerotherapy within the previous 30 days and those whose follow-up was not considered to be feasible were ineligible