Low molecular weight heparins are in European countries the standard of treatment for deep venous thrombosis. Initially the use of low molecular weight heparins was derived of the use of unfractionated heparin: two daily subcutaneous injections with a biological adaptation on anti-Xa activity. However, rapidly, the safety of a fixed dose based on the weight was demonstrated and the biological control is no more recommended. A new low molecular weight heparin, tinzaparin, has proved its efficiency in once a day injection, several published trials have demonstrated similar results with others low molecular weight heparins. Thus the treatment of patients with deep venous thrombosis as out patients is actually a major alternative. In the future long term treatment of venous thrombosis with low molecular weight heparins could be an alternative to the oral anticoagulation. Trials in pregnant women is an emergency, low molecular weight heparins are theoretically the ideal approach for treatment of deep venous thrombosis during pregnancy. Finally low molecular weight heparins are different but the clinical implications of theses differences is still an open question.