Gray scale ultrasound evaluation of the inferior vena cava is essential for adequate workup of abdominal tumors. Demonstration of perivascular nodal masses and/or invasion of the inferior vena cava is of prognostic significance and of value in planning the surgical approach. In addition, accurate delineation of the extent of such tumor invasion by ultrasonography may preclude additional study by more invasive diagnostic procedures, such as angiography. Results of ultrasonic examination of six patients are reported; all were shown to have significant mass effects on the inferior vena cava.