Percutaneous nephropyelostomy is commonly performed prior to endoscopic procedures, such as percutaneous nephrolithotomy or endopyelotomy. We report a case of colonic perforation, complicating percutaneous nephrostomy, which was managed conservatively. A 10-year-old girl was admitted to our hospital for the diagnosis of ureteropelvic junction obstruction. The first percutaneous nephrostomy with sonographic guidance was performed for evaluating renal function. About three weeks later, the second percutaneous nephrostomy with fluoroscopic guidance was performed for endopyelotomy. The tract was dilated to 26F incision was made at the ureteropelvic junction without any problems. A nephrostogram, taken 53 days later, revealed a large amount of contrast material in the colon. Abdominal CT scan showed that the nephrostomy tube had passed through the most posterior aspect of the ascending colon. A double-J ureteral stent was placed and the nephrostomy tube tip was withdrawn to lie in the colon. A retrograde pyelography, taken next day, showed no communication between the colon and the right kidney. After 2 days, the tube was removed and no further complications occurred. Reports of percutaneous iatrogenic colonic perforation are rare. The etiology and treatment of this complication are discussed.