There have been many reports on the recognition of vowels by cochlear implant patients fitted with various devices. Most of these reports, however, used a single male and/or female talker to test vowel recognition. This paper presents results on the recognition of vowels produced by a large number of men, women, and children [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099--3111 (1995)]. The aim of this study was to investigate why certain groups of speakers, e.g., children, and certain vowels are harder for the cochlear implant patients to identify. A total of 5 Ineraid patients who had been fit with continuous interleaved sampling (CIS) signal processors were used in this study. Patients' performance on vowel recognition ranged from 54% to 84%. The sex and age of the talker (that is, the talker's vocal tract size) seemed to have a significant effect on the performance for some of the patients, and in particular the ``poor'' patients. Individual patient's results on vowel recognition, and a detailed analysis of the vowel confusions will be presented.