Intravascular leiomyosarcomas of the femoral vein are extremely rare. Our patient was initially diagnosed with a deep vein thrombosis based on ultrasonography and venography. The thrombectomy specimen consisted of typical spindle cells with variable anaplasia arranged in a fasciculating and interlacing pattern. The final diagnosis was proved to be an intravascular leiomyosarcoma confirmed by immunohistochemical studies for smooth muscle actin, desmin, vimentin, CD34 and CD68.