The study examines F1, F2 formant frequencies and duration of all five Greek vowels produced by six Greek speakers with profound hearing impairment and six speakers with normal hearing (three male and three female in each group). The speech material analysed was of the form /'pVCV/ where V=/ i, e, a, o, u /, C=/p, t, k, s/. The study discusses differences in the above acoustic parameters as a function of hearing level, gender, stress and context. The results show longer vowel durations and a reduction of the vowel space for the speakers with hearing impairment. Significant variability due to stress and context was evident between the two groups. The paper discusses findings with reference to perceptual constraints affecting the speech of individuals with hearing impairment.