Hydronephrosis is often caused by urinary tract obstruction, so the treatment of hydronephrosis should be based on the cause, which is to remove the urinary tract obstruction. The common causes of urinary tract obstruction are stones, tumors, congenital stenosis, or prostate enlargement in the elderly and a series of other causes. For stones, extracorporeal shock wave lithotripsy or surgery can be used to remove the stones. If the stone is caused by a tumor, especially in the ureter, you can choose to remove one ureter; if it is caused by congenital stricture, you can choose to put in a double J tube; if it is caused by prostatic hyperplasia in the elderly, you can put in a catheter.