An association between familiar goiter and deafmutism was first reported two deaf-mute sister with pronounced gioter in 1896 by Pendred, an English practitioner. Thereafter Morgan and Trotter(1958) demonstrated a specific enzymatic defect as the cause of the goiter and Fraser(1965) defined Pendred's syndrome as a triad : congenital perceptive hearing loss, goiter and abnormal perchlorate test. In 1972, Illum et al demonstrated with tomography of the inner ear in axial pyramidal projection that a large number of patients suffering from Pendred's syndrome have isolated malformation of the cochlear of a previously well known but rare type named after Carlo Mondini in 1971. The most important feature of the defect is that only the basal turn of the cochlear is retained while the apical turns form a common cavity, which was caused by a fault in the development of the modiolus in the seventh fetal week. The incidence of Pendred's syndrome varies considerably and is rare. According to Fraser, 233 cases of Pendred's syndrome were reported up to 1965, although it is a very rare disease in Korea. Recently the author experienced one case of Pendred's syndrome of 16 year-old female who had marked hearing impairment bilaterally, goiter, and abnormal perchlorate test. It was confirmed by the audiogram, tomography of the inner ear and various analysis including potassium perchlorate discharge test for goiter.