Patient: The fetus was found to have mild hydronephrosis by ultrasound when she was pregnant, and now the child is 4 weeks old. No treatment. Response: Further investigations (e.g. urological MRI) are needed to determine whether the cause of hydronephrosis is due to pelvic-ureteral junction stenosis and whether it is to the extent that surgical treatment is required. If surgery is required, posterior laparoscopic ureteropelvic pyeloplasty is indicated.