Leg thrombosis includes arterial thrombosis and venous thrombosis, and the symptoms of the two types of thrombosis are different. Arterial thrombosis in the legs: Arteries are the vessels of the body that transport blood and oxygen to the end of the limbs. Arterial thrombosis blocks the arterial blood flow, so that blood cannot be supplied to the distal limb tissues adequately/timely, which mainly causes ischemic symptoms in the legs. Pain, pale skin color and decreased skin temperature, weakened or absent arterial pulsation, impairment of leg sensation and movement may occur in the leg, and intermittent claudication and limb color change or even ulceration may occur over time. If the embolism is prolonged, localized limb necrosis may result, and even amputation may be necessary. Venous thrombosis of the leg: The vein is the pathway for blood to return to the heart, and when the vein is blocked by the venous thrombosis, the return of blood to the leg is mainly blocked. As the blood stagnates in the leg, the patient’s leg will become edematous and swollen, and the superficial veins will become dilated and the local skin temperature will increase. Prolonged venous return obstruction can also cause localized ulcers and even infection in the lower extremities; necrosis is less common. Acute complete large vein thrombosis sometimes affects the arterial perfusion of the ipsilateral limb, which can cause local ischemia and even necrosis, necessitating amputation, a condition called femoral cyanosis or even femoral leukomalacia. In addition to the symptoms to determine the leg thrombosis, further ultrasonography, arteriography, and lower limb venous cascade angiography are needed to clarify the cause and location of the lesion and to develop a treatment plan.