Pendred syndrome is an autosomal recessive inherited disorder. Obligatory 
features are profound deafness in childhood and defective organic binding of 
iodine in the thyroid gland. Therefore, goiter is a common symptom. Hypoplasia 
of the cochlea is another feature. Recently, the gene for Pendred syndrome was 
identified. We describe a boy whose sensorineural hearing loss in both ears 
progressed rapidly from about 50 to 60 dB at the age of 3 years and 3 months to 
more than 100 dB at the age of 4 years and 4 months. This loss was preceded by a 
medical history of a progressive hearing loss. The progressive nature of the 
hearing loss motivated a search for the cause. Dysplasia of the cochlea and a 
widened vestibular aqueduct were found. The results of thyroid function tests 
were normal, but he had an elevated level of thyroglobulin. The diagnosis of 
Pendred syndrome was confirmed by the positive results of a potassium 
perchlorate test, indicating defective organic binding of iodine in the thyroid 
gland. It is possible that the widened vestibular aqueduct was responsible for 
the increase in the hearing impairment. Aside from the branchio-otorenal 
syndrome, Pendred syndrome is the only other known genetic disorder with a 
widened vestibular aqueduct. If a child has progressive sensorineural deafness 
and a widened vestibular aqueduct, it is important to consider a diagnosis of 
Pendred syndrome. A widened vestibular aqueduct may help to elucidate the 
pathophysiologic characteristics of hearing loss in these genetic types of 
deafness in childhood.