Renal tumors are the most common malignancy associated with inferior-vena-caval occlusion. The level of obstruction is usually in the middle third of the vena cava. Middle vena-caval occlusion should be suspected when, in addition to the usual signs of inferior-vena-caval obstruction, the presence of albuminuria, hematuria, nephrotic syndrome, or hepatic dysfunction is demonstrated. Four cases presented here illustrate the clinical syndrome. Intravenous urography and inferior-vena-caval roentgenography are the most useful diagnostic aids. Retrograde pyelography, nephrotomography, and renal arteriography may occasionally be necessary.