Inclusion Criteria:  Age 18 years or more Acute thrombosis of varicose great saphenous vein and/or its major branches more than 5 cm from the saphenofemoral junction Signed informed consent  Exclusion Criteria:  More than 3 weeks after symptom onset Ultrasound signs of deep vein thrombosis Suspected pulmonary embolism Superficial vein thrombosis within 5 cm from the saphenofemoral junction Bilateral superficial vein thrombosis Thrombosis of subfascial part of perforating veins to the level of fascia Thrombosis of small saphenous vein Superficial vein thrombosis associated with sclerotherapy History of deep vein thrombosis and/or pulmonary embolism Superficial vein thrombosis within 3 months before inclusion Anemia (haemoglobin less than 90 g/l) Low platelet count (less than 100 X 109/l) Severe renal impairment (calculated GFR less than 20 ml/min/1,73 m2) Body mass less than 50 kg Morbid obesity (BMI higher than 40 kg/m2) Allergy to fondaparinux sodium and local anaesthetics Using anticoagulants for treating the current episode of venous thrombosis Using anticoagulants for other medical conditions (e.g. atrial fibrillation) Double antiplatelet therapy Regular use of NSAIDs (except aspirin less than 325 mg daily) High risk of bleeding according to an investigator Active clinically relevant bleeding Clinically relevant bleeding within last 30 days before inclusion Major surgery of severe head trauma within last 30 days before inclusion Ophthalmic, spinal or cerebral surgery within last 12 months Active gastric or duodenum ulcer, erosive and ulcerative gastrointestinal disorder Documented haemorrhagic diathesis Uncontrolled arterial hypertension (systolic[180 mm Hg, diastolic[110 mm Hg) Active cancer, history of cancer Acute illness, decompensation of chronic illness Autoimmune disease, treatment of autoimmune disease Severe chronic heart failure and/or marked oedema due to heart failure Severe pulmonary insufficiency Bacterial endocarditis Severe renal failure Known severe thrombophilia (antiphospholipid syndrome, a deficit of antithrombin, a deficit of protein C, S, factor V Leiden, prothrombin G20210A) Immobility, unable to increase mobility Pregnant or breastfeeding women Alcohol abuse, drugs abuse or other circumstances indication low compliance Unwilling of unable to follow requirements of the protocol