Whether a 4mm stone in both kidneys needs to be serious depends on the location of the stone. If the stone is in the kidney calyx, which is in the innermost part of the kidney, the only effect on the patient is to cause a small amount of red cells in the urine that can be seen when the patient checks the urine routine. If the patient’s occupation is a pilot or high-risk operation, it may have some impact on the patient’s work because the nature of the job dictates that there cannot be stones. For the average patient, stones do not have any effect. If the stone is located in the urinary tract and causes urinary tract obstruction, it may need to be treated. Such stones of about 4mm can be treated by making the patient drink more water, and if the stones cannot be expelled, they can be treated with the aid of medication. A stone of about 4mm in the kidney may be prone to change in location if it is located in the middle and upper calyces of the kidney, and the stone is likely to expel on its own, causing the patient to experience sudden pain, which requires close follow-up and observation. If the stone is located in the lower calyces of the kidney, i.e., the lowest part of the kidney, no special treatment can be done, and only regular checkups are needed to see if the stone location and size have changed. For patients with stones in the lower calyces, regular ultrasound of the urinary system should be done once every 0.5 to 1 year.