Ureteropelvic junction stenosis is the most common type of ureteral stenosis. Most of them are congenital developmental anomalies, and the causes include factors in the duct itself, such as high openings in the junction, intra-ductal valves, polyps, and torsions. Stenosis of the junction may also result from compression by extra-ductal factors, such as compression of the ureter by fibrous cords or ectopic vessels leading to the lower part of the kidney. In addition, intraluminal renal surgery, such as flexible ureteroscopy, may also damage the connection secondary to stenosis. As the urine produced by the kidney cannot be drained through the narrowed junction in a timely manner, the direct consequence of junctional stenosis is that it leads to hydronephrosis, and prolonged hydronephrosis can impair kidney function and lead to loss of kidney function in severe cases. There are various treatments for pelvic ureteral junction stenosis. Patients with early detection and relatively mild hydronephrosis can be observed. Late detection and severe hydronephrosis leading to loss of kidney function may require removal of the kidney. Most cases can be treated by removing the stricture factor and repairing the ureter. This can be done by cutting through the duct and dilating the stricture segment, while the most effective method is to remove the stricture segment, trim the dilated renal pelvis and re-suture it to the ureter, also known as pyeloureteroplasty.