The objective of this study was to investigate the perceptual relevance of acoustic differences in vowels produced by 6 children between the ages of 9-13 years old with unilateral cochlear implants. Formant frequencies were estimated for 12 repetitions of vowels /hid/, /hed/, /haed/, /hud/, /hUd/, and /hAd/ produced by the children. The estimated formant frequencies were compared with those of age- and gender-matched children from an existing normative database to identify vowels that were within or outside typical ranges. Vowel production was also examined by means of phonemic (broad) transcriptions by trained transcribers. Additionally, 12 listeners with typical hearing identified these vowels in a closed-set identification task. Results showed that the deviations in vowel formant frequencies (i.e., between 1-2 SD and outside 2 SD with respect to normative data) are perceptible to trained as well as untrained listeners and therefore need to be addressed during the (re)habilitation process.