Pelvi-ureteral junction (PUS)/ureteropelvic IUPJ)UPJ obstruction is the most common obstructive lesion in childhood and is the most common cause of hydronephrosis found on prenatal and early postnatal ultrasonography. • It is most commonly caused by intrinsic stenosis of a segment of ureter which is usually localized to the region of pelviureteric junction. Other causes include ureteric folds & extrinsic obstruction by crossing lower pole vessels.PresentationHydronephrois revealed by maternal USG (Dilated renal pelvis but normal ureter). Palpable renal mass in new horns or infants. Abdominal flank or back pain typically exacerbated by drinking large volumes of liquid. UTUHaemanuia after minimal trauma. Epidemiology Left side more commonly involved than right (Bilateral = 10%). Male more commonly involved than females (M : F = 2 : 1). Initial iagnosis by Ultrasonography Hydronephrosis with dilated renal pelvis. Ureter if visualized is of normal caliber (not dilated).Renal Differential function Nuclear Renography is used to determine Renal Differential functionA differential function of < 40% is considered significant and often an indication for surgical management. Management Management depends on the differential renal function and AP diameter of PUJ :-Differential renal function > 40% especially when AP diameter ofPILI <30 min -3 Conservative treatment. Differential renal function < 40% especially when AP diameter of PUI > 30 MM —4 Surgical treatment is indicated. Pyeloplasty is the surgical procedure of choice. Other surgical procedures used are external drainage (nephrostomy), endopyelotomy and nephrectomy.Differential function of < 10% is often considered as an arbitary cut off for nephrectomy.