Reduced left kidney size may be caused by congenital left renal dysplasia, left chronic pyelonephritis and other diseases, which cause left kidney atrophy, and left renal artery stenosis can also lead to left kidney size reduction. Reduced volume of the left kidney is clinically known as left renal atrophy, the cause of this disease is more complex, if the patient has congenital left renal dysplasia and other congenital renal diseases, usually at birth will find the left kidney volume reduced. Urologic diseases such as left chronic pyelonephritis and left renal artery stenosis may also lead to left renal atrophy. There may be other reasons for the decrease in the size of the left kidney, so it is recommended that patients go to regular hospitals in time, complete the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.