For stone 4mm, it is not serious in general, only very few cases are very serious. If the stone is 4mm located in the kidney, in this case you can drink more water and exercise more, and most patients are able to excrete the stone on their own. If the ureteral stone is 4mm, some patients will be embedded in the inner part of the ureteral bladder wall, because the inner part of the ureteral bladder wall is narrow and the ureter is only about 2-3mm, in this case, the 4mm stone can be expelled from the body through the effect of antispasmodic discharge. However, there are some patients with 4mm stones embedded in the inner part of the ureteral wall for a long time, which will cause serious hydronephrosis and even damage to kidney function, which is the most serious case.