Aged patients with atrial fibrillation (AF) are at high risk of both thromboembolic and hemorrhagic complications of the disease and its treatment. A study was conducted to assess the role of the D-dimer plasma level as a marker of thrombosis in aged patients with AF having no clinical signs of active thrombosis with respect to the used treatment strategy and the quantitative thrombotic and hemorrhagic risk of AF. The results show that the D-dimer plasma levels correlate with the scores of thromboembolic and hemorrhagic risks in groups on antiplatelet agents but not anticoagulants, with the difference in D-dimer level driven by a subgroup on CHA2DS2-VASc point ≥5. A high D-dimer level was associated with in-hospital mortality and AF rhythm at the moment of blood sample collection. Therefore, the accuracy of risk prognosis for fatal complications of AF in elderly patients may be increased with the use of the laboratory markers of thrombus formation such as the D-dimer level and with the use of the obtained results as a guide to antithrombotic therapy.