We described a patient with progressive non-syndromic hearing loss (NSHL) harboring the A3243G mutation in the mitochondrial DNA (mtDNA). Muscle biopsy showed scattered ragged-red, cytochrome c oxidase negative fibers, whereas the biochemical analysis of the mitochondrial respiratory chain complexes was normal. Restriction fragment length polymorphism (RFLP) analysis showed A3243G mtDNA transition, present at very low in patient's muscle (3%) and in urinary sediments (1%), and not detectable in blood and buccal mucosa. The patient was submitted to a bilateral cochlear implantation with post-operative excellent hearing and communicative outcomes. Our findings indicate that A3243G mutation may be responsible both for SHL and NSHL, may be depending on the levels of mutated mtDNA. Patients with hearing loss due to mtDNA mutations should be considered as good candidates for cochlear implantation.