Upper torso deep vein thrombosis usually occurs in association with an indwelling venous catheter and/or malignancy as part of a paraneoplastic syndrome. However, idiopathic internal jugular vein thrombosis is a rare but potentially fatal condition. We report a 59-year-old woman who presented with severe dizziness. Ultrasonography and contrast-enhanced multislice computed tomography revealed thrombi in the left internal jugular vein. This patient had no malignancy, coagulation disorder, or infection. A ventilation/perfusion scan of the lungs showed no evidence of pulmonary embolism. This is a rare case of idiopathic thrombosis of the internal jugular vein.