Patients with ovarian cancer with clear cell histology often have venous thromboembolism (VTE) even before surgery. In view of the possible association between clear cell histology and VTE in endometrial cancer, we measured the plasma levels of thrombin-antithrombin III complex (TAT) and D-dimer (DD) in the preoperative examinations of a patient with clear cell adenocarcinoma of the endometrium. Plasma TAT and DD were both highly elevated, though the patient had no symptoms of VTE or risk factors such as obesity or diabetes mellitus. Ultrasound Doppler examination and lung perfusion scintigraphy just before surgery revealed a thrombosis in the left popliteal vein and a pulmonary embolism. After implanting an inferior vena cava filter to prevent a fatal embolism of the lung, we performed abdominal total hysterectomy, bilateral salpingo-oophorectomy, and sampling of the pelvic lymph nodes. The VTE gradually disappeared and the plasma levels of TAT and DD returned to normal after surgery. Possibly, the VTE in this patient may have been associated with the clear cell histology.