Abstract: This study investigated the acoustic characteristics of the Belgian Standard Dutch vowels in children with hearing impairment and in children with normal hearing. In a balanced experimental design, the 12 vowels of Belgian Standard Dutch were recorded in three groups of children: a group of children with normal hearing, a group with a conventional hearing aid and a group with a cochlear implant. The formants, the surface area of the vowel space and the acoustic differentiation between the vowels were determined. The analyses revealed that many of the vowels in hearing-impaired children showed a reduction of the formant values. This reduction was particularly significant with respect to F2. The size of the vowel space was significantly smaller in the hearing-impaired children. Finally, a smaller acoustic differentiation between the vowels was observed in children with hearing impairment. The results show that even after 5 years of device use, the acoustic characteristics of the vowels in hearing-assisted children remain significantly different as compared to their NH peers. (C) 2015 Elsevier Inc. All rights reserved.