Five cases of extension of renal carcinoma into the inferior vena cava were detected using gray scale ultrasonography. Two different ultrasonographic appearances reflecting the intracaval tumor were observed. Four patients had one or two intraluminal echogenic nodules or thrombi, and the fifth case manifested generalized caval dilatation with innumerable diffuse low amplitude echoes emanating from the lumen. The role of ultrasonography in the complete evaluation of the patient with renal carcinoma is discussed, and the ultrasonographic features of intracaval tumor are demonstrated.