Six cases of malignant abdominal neoplasm with extensive tumor involvement of the veins form the basis of this report. One case was a child with retroperitoneal liposarcoma. Proper therapeutic management in these cases was dependent upon a complete angiographic evaluation, including cavography. This procedure is virtually without complications and should, therefore, be done routinely in cases of abdominal neoplasms for evaluation of the operability, to confirm the angiographic findings indicating intravenous tumor invasion or extravenous compression, and as a primary examination in the assessment of possible or known abdominal tumors in children.