A 15-year-old Japanese boy was transported to our hospital because of right abdominal pain and gross hematuria that occurred after a ball hit his right abdomen during a soccer game. Abdominal US revealed large right hydronephrosis. Laboratory data revealed serum creatinine and hemoglobin levels of 1.48 mg/dL and 12.8 g/dL, respectively. Urinalysis revealed numerous red blood cells. CT revealed right hydronephrosis beyond the center of the spine and did not detect the left kidney. He underwent an immediate percutaneous nephrostomy with a 12-Fr catheter and was relieved of the abdominal pain. However, 6 h later, the catheter was obstructed by a blood clot. Therefore, 1 day later, the nephrostomy was dilated by a 16-Fr catheter. Twelve days later, antegrade pyelography was performed to identify the position and length of the obstruction in the right ureter; the pyelogram obtained showed relieved expansion of the right renal pelvis and calyx and a PUJO. Thereafter, CT was performed, which revealed a cyst that was separated from the right renal pelvis adjacent to the right kidney. This cyst was speculated to be the cause of the right ureteral obstruction; however, we could not confirm this. Renal dynamic scintigraphy with Tc-99m diethylenetriaminepentaacetic acid revealed a right renal obstructive pattern and a left non-functioning kidney. One month after the nephrostomy, he underwent cystoscopy and bilateral retrograde pyelography. Cystoscopy revealed normal bilateral ureteral orifices, while bilateral retrograde pyelography revealed a right PUJO with a clot-associated pelvic filling defect and the blind end of the left ureter in the pelvis. Accordingly, he was diagnosed with a right PUJO and a left hypoplastic kidney. He was scheduled for a right pyeloplasty 5 months after his first visit. Under general anesthesia, a right ureteral stent was placed prior to the pyeloplasty procedure. The patient was placed in a supine position, and a ventral incision was made. The ascending colon was mobilized by incising the lateral peritoneum, and the right ureter was identified. The right ureter at the ureteropelvic junction was peeled from the surrounding tissues, and no stenosis was observed in it. The left ureter was thread-like over a length of 4 cm, and the left renal pelvis was cystically expanded. A left dismembered pyeloplasty was then performed, and a ureteral stent was placed in the left ureter. The operation revealed a left crossed and fused ectopic kidney; left pelvic expansion secondary to right hydronephrosis-associated left PUJO was also observed. Twelve months after the operation, CT revealed shrinkage of the right renal pelvis and calyx. Twenty-four months later, there was no recurrence of abdominal pain and gross hematuria, and the serum creatinine level was maintained at 1.1 mg/dL.