Objective: The purpose of this study was to compare vowel productions by deaf cochlear implant (CI) children, hearing-impaired hearing aid (HA) children and normal-hearing (NH) children. Patients and Methods: 73 children [mean age: 9;14 years (years;months)] participated: 40 deaf CI children, 34 moderately to profoundly hearing-impaired HA children and 42 NH children. For the 3 corner vowels [a], [i] and [u], F1, F2 and the intrasubject SD were measured using the Praat software. Spectral separation between these vowel formants and vowel space were calculated. Results: The significant effects in the CI group all pertain to a higher intrasubject variability in formant values, whereas the significant effects in the HA group all pertain to lower formant values. Both hearing-impaired subgroups showed a tendency toward greater intervowel distances and vowel space. Conclusion: Several subtle deviations in the vowel production of deaf CI children and hearing-impaired HA children could be established, using a well-defined acoustic analysis. CI children as well as HA children in this study tended to overarticulate, which hypothetically can be explained by a lack of auditory feedback and an attempt to compensate it by proprioceptive feedback during articulatory maneuvers.