There are over 60 types of hereditary hearing loss in man and most of these are distinguished from one another by outstanding associated defects caused by the same gene producing hearing loss. However, there are at least 12 types of hereditary hearing loss with no known associated defects. The authors experienced two similar families with hereditary hearing loss. The affected offsprings had inevitably and affected parent in the type of transmission(autosomal dominant) and the hearing loss developed in childhood and progressed. Audiologic findings showed bilateral symmetrical moderate to severe sensorineural hearing loss with flattened configuration on the audiogram. Otologic vestibular function tests showed no abnormal finding and the associated anomalies couldn't be observed in history or clinical examinations.