Stenosis of the ureteropelvic junction is a common congenital obstructive lesion and is the most common cause of hydronephrosis in pediatric and adolescent patients. It is seen in all age groups, but has a greater incidence in children and males, mostly on the left side. Bilateral lesions are seen in up to 40% of cases. The clinical presentation varies by age, with pain, hematuria or infection seen mostly in children, while in infants an abdominal mass predominates and hematuria is seen mostly after mild trauma. Another characteristic is back pain after drinking large amounts of water, indicating that the renal pelvis is suddenly dilated by diuresis, causing pain. Painful episodes may be accompanied by nausea, vomiting, hematuria, urinary tract infection, and hypertension. Bilateral lesions may eventually progress to bilateral hydronephrosis and uremia. Ultrasound can reveal dilated hydronephrosis and thinning of renal parenchyma. Prenatal ultrasound can help detect hydronephrosis at an early stage. Prenatal ultrasound can help to detect hydronephrosis at an early stage. Pyelogram shows delayed visualization of the affected renal pelvis, dilated renal pelvis and calyces, and obstructed excretion of contrast agent in the ureteral junction of the pelvis. The ureteral diameter was normal. Retrograde contrast combined with pyelogram can clearly show the stenotic lesions in the pelvic ureteral junction. Prevention and treatment measures: 1. For mild hydronephrosis, follow-up observation can be continued for 3-6 months, but if the hydronephrosis worsens, further treatment is required at a regular hospital under the guidance of a specialist. 2. Avoid urinary tract infections and holding urine. 3.If you have any uncomfortable symptoms, go to the regular hospital at any time and perform pyeloplasty if the hydronephrosis is serious. The purpose of pyeloplasty is to release the narrow ureteral area, so that the pelvic urine can be removed smoothly, reducing the pressure on the pelvis and relieving pelvic fluid, but it should be clear that pelvic fluid does not disappear completely after surgery. 4, pay attention to the protection of the kidney area, to prevent extrusion by external forces, resulting in hydronephrosis kidney damage or even rupture. 5.Regularly perform ultrasound or intravenous pyelogram to understand whether there are obvious changes in hydronephrosis.