Recent studies on the treatment of acute deep vein thrombosis (DVT) with low-molecular-weight heparins have demonstrated that a certain degree of early recanalization of thrombosed veins can be obtained which is higher than that observed under standard heparin treatment. Thrombolytic treatment of DVT is mainly advocated because a reduction of late sequelae of DVT is expected from early thrombolysis. It has been made likely by several small long-term studies that this expectation is true, but conclusive evidence is still missing. There are also large differences in the reported incidence of late postthrombotic syndrome after acute DVT. It seems likely that there is a minimal reopening rate which is required to be of possible clinical value to the individual patient. A 30% or higher reduction of the Marder score is at present used in several clinical trials as a sign of individual response to the treatment and may prove to be a useful clinical endpoint in these and in future studies. Validated methods to predict the late sequelae of acute DVT, mainly severe postthrombotic syndrome, do not yet exist. Foot plethysmography, air plethysmography, duplex sonography (peak velocity of venous reflux, valve competence), and venous pressure reduction under exercise are possible candidates to be used in future prospective trials. From the existing evidence it is very likely that a marked or total reduction of thrombi will reduce the incidence of postthrombotic syndromes. Clinical studies aiming at a high rate of venous recanalization by prolonged treatment with low-molecular-weight heparins are ongoing.