Both polycystic kidney and renal cysts can appear as cysts under ultrasound, but the diagnostic criteria and the effects on kidney function and prognosis are completely different. Polycystic kidney disease is a hereditary disease with a 50% chance of inheritance, and the consequences are more serious. The main diagnostic criteria are related to age, among patients aged 15-40, there are at least three cysts in unilateral or bilateral kidneys under ultrasound. 40-69 years old patients with at least two cysts each in bilateral kidneys, over 60 years old patients with at least four cysts each in bilateral kidneys can be diagnosed, while over 40 years old patients with less than two cysts in bilateral kidneys can be excluded. So polycystic kidney has many more cysts under ultrasound than kidney cysts. Kidney cysts are often single or less than two cysts, and simple kidney cysts will not lead to abnormal urinalysis and kidney function damage, while in patients with polycystic kidney over 60 years old, 50% of patients will lead to the occurrence of kidney failure. Therefore, it is usually necessary to have regular medical checkups to detect kidney lesions in time.