The most common form of non-syndromic autosomal recessive deafness (NSRD) is caused by mutations in the GJB2 gene. Recently, a deletion truncating the GJB6 gene, called del(GJB6-D13S1,830) has also been described normally accompanying mutations in another allele of the GJB2 gene. Among all the mutations described to date, 35delG in the GJB2 gene is the most common. Preliminary data suggest that pathologic changes due to GJB2 mutations do not affect the spiral ganglion cells, which are the site of stimulation of the cochlear implant. Besides, the survival of the spiral ganglion cells is believed to be an important determinant of the outcome after surgery. Therefore, we have studied 49 non-syndromic deaf patients with unknown etiologies in order to determine the prevalence of GJB2 and GJB6 gene mutations in patients undergoing cochlear implantation surgery. Also, the molecular studies were performed using polymerase chain reaction amplification and direct sequencing. As a result, we found 19 individuals with GJB2 mutation including one new mutation (K168R), one patient homozygous for the del(GJB6-D13S1,830). These results establish that genetic screening can provide an etiologic diagnosis, and may help with prognosis after cochlear implantation, as has been hypothesized in previous studies.143A1580-2