The importance of monitoring renal function in patients undergoing cystectomy and urinary diversion is well established. Dynamic renography using Tc-99m MAG3 in combination with furosemide challenge has been widely used to determine the differential function of the kidneys, occurrence of reflux as well as the patency of the outflow tract in this context. The authors have described here a patient in whom significant urinary reflux from the neo-bladder into the nonfunctioning kidney was demonstrated during MAG3 diuretic renography.