The size of the kidneys rarely draws attention to the fact that it is an issue that is relevant to the future of kidney disease and to life. Talking about the size of the kidney is intended to deepen the reader’s awareness and attention, and the discovery of abnormalities will lead to a deeper insight, favoring early prevention and proper treatment. To illustrate its significance, let’s start with a few real-life stories. Although Xiao A usually has recurrent urinary frequency, urinary urgency phenomenon, seems to be no big deal, and does not affect the work, and did not purposely go to the doctor, one day suddenly lumbar abdominal pain, no urine, to the hospital for examination, the problem is quite serious, the left kidney is completely non-functional, the right kidney enlargement with fluid, and finally judged to be due to renal tuberculosis. Xiao B, who had always been diligent and studious, and whose family did not notice any abnormal discomfort, vomited frequently even after his fever had subsided, and was examined at the hospital, where he found that both kidneys had shrunk. Example three is an old man in his sixties, hypertension for 10 years, usually still in good health, once the stomach, vomiting and diarrhea for 2 days, several days after taking drugs and injections, the condition is more serious, blood tests suggest uremia, is acute or chronic uremia? There are two different opinions, because the outcome of the two is very different from the good and evil, the result is that the ultrasound measurement of the kidney enlarged and closed the case. Case 4 was found to have hypertension when he was in college, but he thought that the disease ran in his family and was not taken seriously. After further investigation, it turned out that his hypertension was not hereditary but was caused by ischemia of the right renal artery due to stenosis of the kidney, which led to hypertension, and the right kidney shrunk due to ischemia. Although the measurement of kidney size cannot directly find the cause of kidney disease, it can provide a preliminary understanding of the nature of the lesion, draw the doctor’s attention, or differentiate between acute and chronic diseases, and provide the basis for reasonable treatment. For example, the enlarged right kidney of Little A is caused by fluid accumulation, and what is the cause of fluid accumulation? Example 2, Little B’s kidneys have shrunk, indicating that the disease has been a long time, missed the time for treatment, can only rely on dialysis instead of kidney work; Example 3, the old man’s kidneys swollen, suggesting the existence of factors that cause acute renal failure (also known as acute kidney damage), reasonable treatment can still improve; Example 4, but fortunately did not miss the opportunity to check the size of the kidneys, otherwise, the need for long-term antihypertensive drugs, the side effects of drugs aside. The side effects of drugs aside, due to long-term renal ischemia makes the right kidney gradually atrophy hardened, lost the opportunity to recover, hypertension can never be cured, more unfortunate is the long-term hypertension, and eventually the healthy left kidney also followed by hypertensive nephrosclerosis, ending in chronic renal failure. There are various methods to measure kidney size, B-mode ultrasonography is the easiest and most convenient, and economical, and should be used as a routine item in physical examination. The B-mode ultrasound method of kidney size measurement includes the long diameter of both poles of the kidney and the parenchymal thickness of the kidney. The length of the kidney varies according to ethnicity, height and age, with the left kidney slightly longer than the right kidney and men slightly larger than women. According to the survey of our population, the kidney length diameter of adults is roughly 10-12cm, 5-6cm wide; the kidney volume of the elderly decreases with age, the survey concluded that the kidney length diameter of the elderly is 9.2cm-11.8cm, <9.2cm for the kidney shrinkage, >11.8cm for the increase. The thickness of renal parenchyma in adults is about 1.5-2cm, and there is no significant difference in the elderly, <1.5cm is shrinkage, >2.0cm is thickening. According to the survey, the kidney length diameter plus renal parenchymal thickness measurement to identify acute and chronic renal failure, the compliance rate reached 92.6%. With chronic kidney disease, regular measurement of kidney size can help monitor the progression of the lesion.