Whether a kidney cyst of 4 centimeters is serious or not depends on whether the kidney cyst has compressed the renal pelvis and caused hydronephrosis and back pain and other related symptoms. Usually, if there are no symptoms, it is not serious, but if there are compression symptoms or other complications, it is relatively serious. Renal cyst is a benign lesion, the specific cause is not particularly clear, it may be the cystic cavity formed during the development of the renal tubules, but also related to infection, stones and other diseases. Kidney cysts with a diameter of 4 centimeters, if there are no symptoms and no pressure on the renal pelvis, they are usually not serious and do not need to be treated, and regular checkups are sufficient. If the cyst has pressure on the renal pelvis, resulting in hydronephrosis, or the cyst is infected, timely surgical treatment should be carried out, and the surgery is usually puncture or laparoscopic decompression of renal cysts. It is recommended that patients with renal cysts should go to the hospital in time and follow the doctor’s instructions for regular review or surgical treatment.