For some patients, genetic testing can reveal the etiology of their hearing impairment, and can provide evidence for a medical diagnosis. However, a gap between fundamental genetic research on hereditary deafness and clinical otology emerges because of the steadily increasing number of discovered genes for hereditary hearing impairment (HHI) and the comparably low clinical differentiation of the HHIs. In an attempt to keep up with the scientific progress, this article enumerates the indications of genetic testing for HHI from a clinical point of view and describes the most frequently encountered HHIs in Belgium. Domains of recent scientific interest, molecular biological aspects, and some pitfalls with HHIs are highlighted. The overview comprises bilateral congenital hearing loss, late-onset progressive high frequency hearing loss, progressive bilateral cochleo-vestibular deficit, and progressive low frequency hearing loss. Also, several syndromal forms of HHI are summarized, and the availability of genetic tests mentioned. Finally, the requirements for successful linkage analysis, an important genetic research tool for localizing the potential genes of a trait on a chromosome, are briefly described.