Despite the increased effectiveness of modern diagnostic methods to distinguish benign from malignant renal lesions, surgical exploration remains indicated in all patients who demonstrate a renal mass or tumor deformity of the collecting system on urographic studies and present a reasonable surgical risk. Selective renal angiography represents the most sensitive preoperative method of demonstrating probable malignant changes in suspicious renal lesions. However, absence of such changes cannot be regarded as conclusive evidence ruling out malignant neoplasm. Since the potentially more curable, small, relatively avascular renal tumors are less reliably demonstrated by angiography, a possible diagnostic error of 3% to 5% is not an acceptable substitute for surgical exploration. Nine selective patients from our experience of over 300 renal mass angiograms are presented who illustrate the limitations of this procedure.