The significance of left renal pelvis separation or right renal pelvis separation is basically the same. The so-called renal pelvis separation is found and reported during ultrasound examination of the kidney. Under normal circumstances, the separation of the renal pelvis is less than 1 cm. If the separation of the pelvis is greater than 1 cm, it indicates the presence of hydronephrosis. The human urinary system is composed of kidney, ureter, bladder and urethra. When any part of the ureter below the ureter, such as congenital malformation, urinary stones, tumor, inflammatory stricture, etc., there will be different degrees of hydronephrosis, which will be shown as pelvic separation on ultrasound. Especially in patients with lower urinary tract obstruction, such as prostatic hyperplasia and urethral stricture in elderly men, bilateral pelvis separation and hydronephrosis can occur at the same time. Of course, there is a physiological phenomenon of pot-bellied renal pelvis, which can also manifest as renal pelvis separation. Therefore, after the appearance of renal pelvis separation, it is best to have a comprehensive analysis by a urologist to see if it is clinically significant or not.