The main purpose of this study was to compare acoustically the vowel spaces of two groups of cochlear implantees (CI) with two age-matched normal hearing groups. Five young test persons (15-25 years) and five older test persons (55-70 years) with CI and two control groups of the same age with normal hearing were recorded. The speech material consisted of five German vowels V = /a[modifier letter triangular colon], e[modifier letter triangular colon], i[modifier letter triangular colon], o[modifier letter triangular colon], u[modifier letter triangular colon]/ in bilabial and alveolar contexts. The results showed no differences between the two groups on Euclidean distances for the first formant frequency. In contrast, Euclidean distances for F2 of the CI group were shorter than those of the control group, causing their overall vowel space to be compressed. The main differences between the groups are interpreted in terms of the extent to which the formants are associated with visual cues to the vowels. Further results were partially longer vowel durations for the CI speakers. (Contains 1 table and 3 figures.)