A retro-renal colon (RRC) is a rare but important anatomical variant to consider when planning percutaneous stone surgery. CT scanning of the abdomen is critical to detect this and to plan the surgical approach to avoid injury to the colon. In this case report, a 38-year-old woman with large obstructing bilateral symptomatic renal stones was found to have a left retro-renal colon on image review prior to left percutaneous nephrolithotomy.