Early diagnosis and treatment of deep venous thrombosis (DVT) in the leg is of decisive importance, in particular in view of the potentially life-threatening complication of pulmonary embolism. The establishment of the diagnosis if often difficult since in the early stage symptoms may be non-existent or few (50%). The most important therapeutic measure is compression. Acute medication is initiated within the first 24 hours with unfractionated conventional heparin administered as a continuous i.v. infusion or intermittent s.c. injections. An initial bolus injection is followed by continuous infusion of 30,000-40,000 units of heparin. More recent data show that low-molecular-weight heparins are as effective as conventional heparin and are easier to apply, making acute treatment on an ambulatory basis feasible. Conversion to anticoagulation treatment is effected with gradually increasing doses, and must overlap heparin for at least 4-5 days. The duration of treatment is determined by the nature of the thrombosis, with recommendations ranging from 3 to 12 months. A shortened in-hospital treatment with early mobilization is considered to be of benefit to the patient.