Mitochondrial DNA mutations are undoubtedly a factor that contributes to sensorineural, non-syndromic deafness. One specific mutation, the A1555G, is associated with both aminoglycoside-induced and nonsyndromic hearing impairment. The mutation is considered to be the most common of all mitochondrial DNA deafness-causing mutations but its frequency varies between different Populations. Here we report on the first large screening of the A1555G mitochondrial DNA mutation in the Greek population. The aim of this study was to determine the frequency of the A1555G mutation in Greek sensorineural, non-syndromic deafness patients, with childhood onset. We screened 478 unrelated Greek patients with hearing loss of any degree and found two individuals harboring the A1555G mutation (0.42%). Both cases had been subjected to aminoglycosides. They were prelingual, familial and homoplasmic for the A1555G mutation. One of the Cases Was also found heterozygous for the frequent GJB2 35delG mutation, while the other case was negative, The A1555G mutation seems to be less common than in other European populations. (C) 2009 Elsevier Inc. All rights reserved.