DFNA9 (Deafness Autosomal Dominant 9) is an autosomal dominant hereditary hearing loss which is associated with vestibular deterioration. The most recent genotype-phenotype correlation studies have been conducted more than 15 years ago. Meanwhile, emerging and valuable vestibular tests have been added to the vestibular test battery. These tests were not available at the time of the correlation studies. The aim of this study is to carry out a prospective cross-sectional study on symptomatic and presymptomatic affected carriers of the Pro51Ser (P51S) Coagulation Factor C Homology (COCH) mutation in order to correlate vestibular data using the complete vestibular test battery with the known data on hearing and vestibular function in relation to age.