We typically treat blood clot with anticoagulants such as coumadin. The duration of treatment depends on the cause of the clot which largerly depends on the history and some basic laboratory work-up. Depending on the cause, the treatment duration may last anywhere from 4 months to indefinitely. 4 monts is typically the duration of treatement in patients with incidental DVT's, indefinite therapy is usually implemented in those with coagulation abnormalities which predispose to clot formation. The inbetween are patients with idiopathic DVT's. Once a clot forms, the body may either disolve it by itself, especially while on anticoagulants, or it may form a layer of cells to isolate it from the vasculature. Chronic DVT's, therefore, do not require therapy because they are isolated from the vasculature.