Thickness of one leg and thinness of the other leg is usually related to physiological factors, amyotrophic lateral sclerosis and venous thrombosis, which can be temporarily observed or corrected by medication or surgery according to the cause of the disease. 1. Physiological factors: If one leg is more active while the other leg is less active, one leg may be thin and the other leg may be thick. Considering that it is caused by bad living habits, there is no need to correct it at present, temporary observation is enough, usually improve the living habits in time, the symptoms will be relieved by themselves. 2. Amyotrophic lateral sclerosis: the seriousness of the disease causes muscle atrophy, resulting in two legs of different sizes. After diagnosis, nutritional support is needed, and oral edaravone is prescribed to improve the function of the nervous system. If the muscle atrophy is severe, the symptoms can be improved through functional training. 3. Venous thrombosis: The formation of deep vein thrombosis may cause the legs to be of different sizes and may affect normal activities. It is recommended to elevate the affected limb as soon as possible, and if the condition is serious, thrombectomy can be considered. One leg is thick and one leg is thin, it may also be caused by the lumbar disc herniation compression of the nerve, or peripheral neuropathy, you need to go to the hospital in a timely manner, under the guidance of the doctor’s standardized treatment.