The authors report a radionuclide renal study in a case of obstructive uropathy secondary to an aneurysm of the internal iliac artery. The aneurysm, which appeared as a vascular blush on the radionuclide angiogram, was diagnosed by contrast angiography. The authors are reporting this case for two reasons: (a) an aneurysm of the internal iliac is rare and (b) it is even more rare that such an aneurysm will cause obstructive uropathy. The combination of a vascular blush in the radionuclide angiographic phase of the renal studies associated with obstuctive uropathy should raise the possibility of an aneurysm as the cause of this obstruction.