Considerable differences on the frequencies of the mitochondrial 12S rRNA A1555Gand tRNA(Ser(UCN)) A7445G mutations have been reported in different populations. Our screening of 168 patients coming from independent Turkish families with prelingual sensorineural non-syndromic deafness revealed three deaf children with A1555G (1.8%) but no examples of A7445G. One proband with the mitochondrial A1555G mutation has also evidence for right parietal infarct on a brain imaging study, for which common thrombotic mutations were found to be negative. Conclusion: This study shows that the mitochondrial A1555G mutation is among the significant causes of prelingual non-syndromic deafness in the Turkish population.