**3.5 Riedel's thyroiditis**

Riedel's thyroiditis is a rare condition of unknown etiology occurring in middle-aged women. In this chronic thyroiditis, thyroid follicles are replaced by fibrous tissue. Association with other autoimmune fibrosclerotic disease, i.e., retroperitoneal fibrosis and sclerosing cholangitis, is also found. Initially patients present with goiter with normal thyroid function but later on become hypothyroid. The diagnosis can be made with FNAC, but sometimes biopsy may be required for confirmation.
