A pathologic kidney with hydronephrosis is prone to rupture after minor trauma to the renal pelvis ; however, it is controversial whether drainage, such as nephrostomy and ureteral stenting, should be performed in this setting. Herein we report traumatic rupture of the renal pelvis in 2 patients with ureteropelvic junction stenosis at two centers. Case 1 : A 15-year-old boy sustained a blunt injury on his left back while playing football. His family physician referred the patient to our hospital for suspected left renal injury. Contrast-enhanced abdominal computed tomography showed left hydronephrosis and fluid accumulation in the left retroperitoneal space, which led to a diagnosis of rupture of the left renal pelvis. The patient was treated conservatively ; however, fluid accumulation around the kidney worsened. A ureteral stent was placed, and the patient's renal colic and imaging findings improved. Case 2 : A 13-yearold boy fell and bruised his abdomen while playing soccer. He was unable to walk because of pain, and was brought to our hospital by ambulance. Contrast-enhanced abdominal computed tomography showed left hydronephrosis and fluid accumulation in the left retroperitoneal space, which led to a diagnosis of rupture of the left renal pelvis. A ureteral stent was placed on the same day, and the patient's renal colic improved.