Despite the increasing number of reports of families with hearing impairment and mitochondrial DNA (mtDNA) mutations, the frequency of these mutations as causes of non-syndromic sensorineural hearing impairment (NSSHI) remains unknown. Mutations such as A1555G, A7445G and 7472insC have been found in several unrelated families implying they are more frequent than initially thought. We describe a family with NSSHI due to the presence of the homoplasmic mtDNA A7445G mutation in the tRNASer(UCN) gene. This is the fourth such family described with this mutation, all of different genetic backgrounds. Our study also demonstrates the difficulties sometimes encountered in establishing mitochondrial inheritance of hearing impairment in some families.