Some people find a phenomenon in daily life that the legs are thin in the morning and thick at night, what does it mean? From a medical point of view, thin in the morning is normal and thick at night may exist edema. The formation of this edema and systemic systemic diseases may have some relationship, but the protagonist is a local lesion. According to the clinical manifestation, this phenomenon of fine in the morning and swollen at night is called edema of exertional bilateral lower extremities. When the lower extremities have been sagging for too long or after exertion, edema will appear, but after rest, that is, after a night of adequate rest, this edema will disappear. The main cause of edema is localized atherosclerosis of bilateral lower extremity blood vessels, or incomplete closure of arterial or venous valves, causing blood flow back to the lower extremities to stagnate. When the pressure of the stagnation exceeds a certain level, it will enter from the blood vessels under the tissues and become edema. This is when the patient will feel thicker legs and thinner pants. When after sufficient rest, that is, after a night, the blood in the legs gets back to the legs sufficiently, and the water under the tissues passes through the blood vessel walls into the blood volume, this edema will disappear, so this part of the patient will find that the legs are thinner again in the morning. When this happens, a vascular ultrasound of both lower extremities is needed to clarify whether there is a vascular lesion. If there is no serious lesion, it is necessary to wear elastic stockings or to elevate the lower limbs when sitting or lying down to promote blood return.