Pendrin, first identified in 1997, belongs to a superfamily of anion transporters localized in the thyroid gland, inner ear and kidney. Immunohistochemical studies have shown that pendrin is expressed at the apical surface of follicular thyroid cells, where it acts as a Cl-/I- exchanger regulating the chloride transport from the cytoplasm to the colloid space. In the inner ear, pendrin has been found in the stria vascularis of the cochlea and in the endolymphatic duct and sac, where it functions as a Cl- /HCO-3 exchanger. Finally, pendrin is expressed in the kidney, where it is localized in the apical membrane of type-B intercalated cells and non-A, non-B intercalated cells of the cortical collecting ducts and connecting tubules, where it again acts as a Cl /HCO-3 exchanger regulating the acid-base status and chloride homeostasis. Pendrin is encoded by the PDS gene, which is mapped on chromosome 7 (7q22-31.1). Mutations of PDS lead to the Pendred syndrome, a genetic disorder transmitted as an autosomal recessive trait characterized by sensorineural deafness and goiter. It is reasonable to hypothesize that patients affected by Pendred's syndrome may have disturbances of renal function, especially in the regulation of electrolytes and acid-base balance in stress conditions.