Out of 71 cases of familial deafness visited Kitasato University Hospital Otology Clinic, 50 cases (22 families) were transmitted by Mendelian dominance and were diagnosed as sensori-neural deafness with unknown cause. They were 19 males and 31 females, aged from 2 to 44 years. Clinical observations were performed on these 50 cases by obtaining pure tone audiograms, and the results were as follows.
1) Thirty-one cases showed high-tone loss, 13 cases showed flat or basin-shaped, and there was no low-tone deafness.
2) The threshold of high-tone was not always high in aged patients.
3) Twenty out of 29 cases under 19 years old showed good agreement with symmetry law of hereditary deafness (Langenbeck), but aged patients were devided evenly into symmetry and asymmtry group.
4) The progression of deafness did not take a certain pattern but in various ways, and the authors stressed that serial observations on each case or family might be much help in the estimate of prognosis of familial deafness.