A 36 years old male patient, diagnosed with radial head fracture had conservative treatment with long arm circular cast for one month. After long arm circular cast was removed, swelling of the dorsum of the hand and forearm pain evolved gradually. A venous color duplex ultrasonography revealed an acute thrombus of the right radial vein. After anticoagulant therapy, symptoms decreased significantly. Upper extremity deep venous thrombosis, although not as common as lower extremity deep venous thrombosis, is a clinical entity with considerable morbidity and may lead to pulmonary embolism and post thrombotic syndrome. Early recognition and appropriate treatment is important to prevent these complications. Immobilization is usually known as a risk factor for lower extremity thrombosis and it may also cause thrombosis in upper extremity veins since it causes statis which is among the component of Virchow's triad. This case report was presented to emphasize that upper extremity deep venous thrombosis may be encountered not only in lower extremity but also in upper extremity during and after immobilization period due to arm casts.