Hello, welcome to HCM. Swelling of the ankle on one side is often a result of sprains or strains. Sometimes diseases that affect the entire body, such as heart disease and kidney or liver failure, can result in excess fluid buildup (edema) that is often concentrated in the legs and feet, leading to swelling not only of the ankles but also of the feet and lower legs. This can also occur with obstruction of the venous system, as may occur with pregnancy and obesity. Diseases of the joints, such as arthritis, can also affect the joints of the ankle and foot, leading to swelling of the involved areas. You should visit your doctor to first find out the cause of your symptoms and than further consult specialist accordingly. Wish you good health.