Nearly all genes that have been localized for autosomal dominantly inherited hearing impairment are characterized by postlingual hearing loss that is progressive in nature. This auditory phenotype is in contrast to that of genes localized for autosomal recessive hearing impairment, which generally cause nonprogressive severe-to-profound or profound prelingual hearing loss. In most cases, extended pedigrees have been used to localize autosomal dominant deafness genes, To date, 22 autosomal dominant loci have been mapped, and 10 of these genes have been cloned. The functions of these deafness-causing genes are diverse and include transcription factors, extracellular matrix components, ion channels, cytoskeletal components, and unknown functions. Interesting findings include the unexpected expression pattern of some of these genes and the discovery that in some genes, allele variants can cause either isolated hearing loss or syndromic deafness. The greatest challenge for future research will be identifying additional deafness-causing genes and elucidating their function in the inner ear. Am. J. Med. Genet. (Semin. Med. Genet.) 89:167-174, 1999. @ 2000 Wiley-Liss, Inc.