INTRODUCTIONVitamin D is a fat-soluble vitamin that is synthesized non-enzymatically in the skin and metabolized in the liver and kidneys. It arranges the immune response of the body, acts as a steroid hormone and plays a crucial role in mineral homeostasis and skeletal health. 1 Serum vitamin D levels in the range 30-60 ng/ml (75-150 nmol/l) are considered normal.Deficiency of vitamin D is associated with a variety of bone disorders (rickets, osteoporosis or osteomalacia), skin diseases and autoimmune disorders. 1,2 It also causes increased risk of cardiovascular diseases such as myocardial infarction (MI), heart failure and coronary artery disease. 2-5 Furthermore, deficiency of vitamin D has been reported in arterial diseases, including aortic aneurysm, peripheral arterial disease, arterial calcification and hypertension. [6][7][8][9] Deep vein thrombosis (DVT) is characterized by thrombus formation, usually in the lower-extremity deep venous system, which causes obstruction or occlusion of blood flow in veins. It is considered to be the third most common cardiovascular disease, after ischemic heart diseases and cerebrovascular events. 10 Although the medical and interventional treatment options for deep vein thrombosis have improved nowadays, it continues to pose a serious problem, especially in cases with inadequate treatment. It can lead to pulmonary thromboembolism, venous gangrene, chronic venous insufficiency and post-thrombotic syndrome. 11 The most well-known factors in the etiology of lower-extremity deep vein thrombosis are genetic predisposition, malignancy, history of surgical operation, immobilization, trauma, bone fractures, long journeys and oral contraceptive use. 12 Nevertheless, there may also be other factors that play a role in the etiopathogenesis of deep vein thrombosis.