Hashimoto's disease is characterized by an insidious symmetrical enlargement of the thyroid, which becomes firm but not painful. Antithyroglobulin antibody and antimicrosomal antibody titers are usually high. Microscopically, thyroid acini are almost replaced by great numbers of B lymphocytes. Unlike Grave's disease, there is no antibody against TSH receptors. Gradually, affected patients develop hypothyroidism. Incidence of thyroid antibodies in the serum increases with increasing age. In women above the age of 50, there is a peak incidence of about 25%, in men, it is about 10%.