The pyeloplasty is a surgical procedure to treat kidney obstruction due to congenital or acquired causes. Congenital like congenital stenosis in the Uretero-pelvic junction (UPJ) or due to crossing blood vessels. Acquired causes like UPJ obstruction post stone disease or renal trauma. For the congenital or the acquired causes the principle of the surgery is to remove the UPJ stenosis (the diseased segment of the ureter) and reconnect the ureter to the renal pelvis again. This procedure is known as dismembered pyeloplasty. It was described in 1940 by Anderson and since then still the gold standard procedure regardless of the approach (open, laparoscopic or robotic). One of the principles of the procedure is to 'Splint' the anastomosis, i.e put something across the anastomosis during the healing process that includes internal and external stents. Also there are surgeons even don't believe in keeping anything across the anastomosis, but they leave a nephrostomy tube only that will not cross the anastomosis. In our division at CHP, we believe that we should keep a stent across the anastomosis to help in the healing process and decrease that chance of intra-abdominal urine leak and to increase the chance of success (90-99%). So for the internal stent, we use to approaches to insert it: 1- Retrograde by cystoscopy and this will take 10 minutes before starting the surgical procedure itself and we put the stent under fluoroscopy guidance and this is the commonest way we use now to put the internal stents. 2- ante grade, and this is basically inserting the stent during the surgical procedure itself from the kidney down to the ureter and this is done without fluoroscopy. For the external stent we use one method, we choose were we will leave the stent and then we create a small hole in the kidney and then pull the stent through the hole and then create small hole in the abdominal fascia and then the skin, all this done under direct vision and control. So now the sent is outside the patient and connected directly to the kidney and the renal pelvis, then the distal part of the stent will be inserted across the anastomosis and before closing the renal pelvis (also under vision) toward the ureter. The external stent will be connected at the end of the procedure to a urine bag. The type of the procedure will not affect out choice of the type of the stent, as both stents can be inserted using the open, laparoscopic or robotic approach. No difference in the choice for antibiotics or pain medication, again because we will perform the same exact surgery (open, lap or robotic pyeloplasty) and so the same incisions. All out patients receive pre and post-operative antibiotics and this will not be different in both groups. For the alternative method, simply is choosing the first patient for example for internal stent, the second patient we will use external stent, the third patient we will use internal stent, then external , then internal..etc. We will not choose the patient according to age or sex. Of course after we tell the parents and the patient about the study and they choose not to enroll, we will use the internal stent as we usually do. Basically all the pyeloplasty surgeries (open, Lap or robotic) are done as inpatient. All the patients will spend the night in the hospital with Foley catheter and next day and after full evaluation most of the patients will be sent home. All the pyeloplasty surgeries are done under general anesthesia.