Pendred syndrome is an autosomal recessive disorder characterized by sensorineural hearing impairment, presence of goiter, and a partial defect in iodide organification, which may be associated with insufficient thyroid hormone synthesis. Goiter development and development of hypothyroidism are variable and depend on nutritional iodide intake. Pendred syndrome is caused by biallelic mutations in the SLC26A4 gene, which encodes pendrin, a transporter of chloride, bicarbonate and iodide. This review discusses the controversies surrounding the potential role of pendrin in mediating apical iodide efflux into the lumen of thyroid follicles, and discusses its functional role in the kidney and the inner ear.