Superior vena cava (SVC) syndrome is usually caused by malignant tumors or their lymph node metastases oppressing a SVC. However, we encountered a case of SVC syndrome that was caused by a thrombus in the SVC, which we considered as a manifestation of Trousseau's syndrome triggered by underlying prostate cancer. A 60-year-old man patient complained of facial swelling. Physical examinations suggested SVC syndrome; enhanced CT and MRI demonstrated the presence of thrombus in the SVC accompanied by multiple mediastinal and axillary lymph node swelling. Histological examination of both percutaneous transluminally aspirated thrombus via a catheter through jugular vein and the axillary lymph nodes included metastatic prostate cancer. Although the ultrasonic and MR images were not compatible with the prostate cancer, needle biopsies from the prostate established the diagnosis. The SVC syndrome as an initial manifestation of underlying unknown malignancy and also due to intravascular thrombosis caused by cancer metastasis to the vascular wall is extremely uncommon.