Hereditary hearing impairment affects approximately 0.05% of all children born in the United States. It is most commonly autosomal recessive, nonsyndromic, and monogenic [autosomal recessive nonsyndromic hearing loss (ARNSHL)]. Although the number of disease loci is not known, some estimates exceed 100. Using a strategy of homozygosity mapping to localize ARNSHL genes by screening consanguineous families for chromosomal regions that are homozygous by descent, we have mapped several genes in multiplex, nuclear, consanguineous families in Tamil Nadu, India. From the mean frequency of the ARNSHL genes in this population, the total number of disease genes is estimated to be 57.