Right hydronephrosis means that the right side of the kidney is impaired in the process of excretion of metabolites, so it often suggests that the right side of the renal pelvis has a separation phenomenon. If it is more than 10mm, it is clinically significant, suggesting that there may be mild hydronephrosis. However, if the separation of the renal pelvis is significantly enlarged, there may be severe hydronephrosis, and the ureter may even be twisted morphologically, in which case the surgeon may have to intervene. As to whether it is a congenital abnormality or an acquired factor that causes the obvious hydronephrosis on the right side of the kidney, the clinician may need to use imaging or cystoscopy to assist in the diagnosis, and in some cases, it may be caused by a narrowing of the pelvic-ureteral junction. Most of the mild hydronephrosis may not have any clinical symptoms, but if the hydronephrosis is obvious, sometimes it will be followed by urinary tract infection, and some children may even have renal function damage, so the clinic should pay enough attention to it.