Deep vein thrombosis is a common disease entity to which attention should be paid due to its complication of pulmonary embolism. This disease usually has precipitating factors such as obesity, varicose veins or non-ambulation. Congenital coagulation defects should be suspected if patient has recurrent deep vein thrombosis without identifiable precipitating factors. We report a case of 44-year-old Japanese male, who had three events of deep vein thrombosis within four years. Doppler ultrasound study at the time of the first event showed extensive thrombosis of femoral veins. Coagulation factors study revealed that patient had antithrombin Ⅲ deficiency. This patient's sister in Japan also had this defect. This patient is using warfarin 5 mg daily and has been followed up uneventfully. In patients with recurrent deep vein thrombosis, hereditary coagulation defect should be suspected and warfarin should be used indefinitely.