A Tc-99m MAG3 renal scintigram was performed on a patient with severe renal insufficiency and bilateral ureteral stents. The Tc-99m MAG3 study displayed typical findings for renal insufficiency but also suggested the presence of lower tract obstruction. Moreover, the delayed posterior and posterior oblique views of the abdomen revealed an extrarenal collection of tracer suggestive of a urinary leak. With the help of additional views, this extrarenal activity was proven to be tracer in the bowel and biliary system. Biliary excretion of Tc-99m MAG3 can be prominent in patients with renal insufficiency and could lead to an erroneous diagnosis of urinary leak. Finally, scintigraphic diagnosis of lower tract obstruction may be difficult in patients with renal insufficiency, but some helpful signs may lead to the correct diagnosis.