Hydronephrosis is a common complication of urological diseases, which is usually less serious if detected in time, and needs to be evaluated in conjunction with the primary disease. Based on the size of the dilated renal pelvis and calyces and the degree of separation of the renal collecting ducts, hydronephrosis is generally classified as mild, moderate or severe according to the ultrasound findings of the kidney. There are many diseases that can cause hydronephrosis, like stones, prostatic hyperplasia, urethral stricture, neurogenic bladder, urological tumors, congenital developmental abnormalities, etc. can cause poor urinary excretion, which in turn can lead to hydronephrosis. Hydronephrosis can cause urinary tract infection, blood in urine, and urinary system irritation symptoms (such as urinary frequency, urinary urgency, painful urination), etc. It can also induce urinary stones, renal insufficiency or even uremia, and induce the occurrence of tumors and other diseases, so when hydronephrosis is found, we need to pay attention to it, actively check the cause and treat it in time to avoid very serious consequences. However, some patients with hydronephrosis caused by congenital diseases, such as congenital pelvic ureteral junction stenosis caused by hydronephrosis, if the symptoms are relatively mild and slow to develop, you can have regular checkups, usually about once every six months, and decide whether surgery is needed according to the changes in the condition. In summary, hydronephrosis is often caused by urinary tract obstruction, which is not serious in itself and can be improved quickly until it is cured, while most of the congenital hydronephrosis with insignificant progress does not require treatment.