One leg is thick and the other is thin, which is usually caused by congenital developmental abnormality, leg trauma, varicose veins and so on. 1. Congenital developmental abnormality: It may be congenital developmental problems, such as suffering from congenital hip dislocation, polio, etc., which may lead to poor development of the legs, and one leg is thick and the other is thin. 2. Trauma to the leg: After the trauma to one side of the calf, not paying attention to the exercise of muscle strength, it may lead to muscle wasting atrophy of the affected limb, so the calf is thicker and thinner. 3. Varicose veins: due to the weakness of the calf vein wall or calf vein valve defects, resulting in varicose veins in the calf, will make the blood return obstruction leg thicker, so the calf one leg thicker and one leg thinner. Different thickness of calves may also be caused by other reasons, it is recommended that patients go to the hospital in time to clarify the cause, and follow the doctor’s instructions for treatment.