This is prospective study to compare the post-operative pain, stent tolerance, stent care and total cost of a common procedure in pediatric urology which is pyeloplasty. The patients will be randomized into 2 groups. All female subjects will undergo a standard urine pregnancy test to rule out pregnancy. The first group will be patients who will have internal Double-J stents and the second group will be patients who will have external Pippi-Salle nephron-ureteric stent. The parents and the patient will be informed at the day of the surgery about the type of stent he/she will have at the end of the surgery. In the post-operative period, the patient will stay overnight (as for all the non-study patients) and next morning his/her Foley catheter will be removed. The patient and his/her family will receive instructions about the care for external stent (if he/she has one) and receive the regular prescriptions for pain medicine and Oxybutynin (if the patient has internal stent). All patients will be given contact information to call in case they have concerns or questions about the study, the procedure itself or the stents.