1. We discuss previous casuistic reports published until now on twins suffering from hereditary deafness of the dominant type.
2. One case of hereditary deafness in a pair of monozygotic twins is reported, the twins showing no considerable difference in their acustical defect.
Prove that deafness in this case was conditioned by heredity and did not arise from an explosion, is given by the mono-zygozity of the patients.
3. It is imperative that each case of questioned hereditary deafness described above should be controlled by audiometric test.