D-dimer antigen is a fibrin degradation product that is formed by the sequential action of three different enzymes on cross-linked fibrin. As such, increased levels of plasma D-dimer should be reliable indicator of thrombus formation. The D-dimer antigen is a specific marker of fibrin clot formation and fibrinolysis, which serves as a clinically useful marker for exclusion of VTE, and evaluation of the risk of VTE recurrence. The monoclonal antibodies raised against specific epitopes on D-dimer react with cross-linked fibrin, but not with fibrinogen degradation products or non-cross-linked fibrin degradation products, thus ensuring high specificity of the D-dimer as a biomarker of fibrin formation and stabilization. The D-dimer measurement methods and literature knowledgeÕs on its diagnostic importance are summarized in this paper.