Nuclear medicine biliary studies have been routinely used to identify bile leaks that occur after laparoscopic cholecystecomy. The use of a Tc-99m mercaptoacetyltriglycine (MAG3) renal scan to diagnose a case of urinary leakage that occurred after a laparoscopic-assisted colectomy is shown in this report. Laparoscopic surgery is widely used in place of conventional laparotomy to minimize recovery time and discomfort after surgery. The complication rate for laparoscopic colectomy has been reported as approximately 6% to 10%. In particular, ureteral leak has been reported in 2% of procedures. Ascites of unknown origin can become a diagnostic dilemma. We present a case of postoperative ascites of unknown origin that was successfully diagnosed as urinary leakage using renal scintigraphy.