OBJECTIVE: To investigate the phonetic inventory development in a group of profoundly hearing impaired children fitted with the 22-electrode cochlear implant (Cochlear Ltd, NSW, Australia) at < or = 5 years of age. BACKGROUND: The cochlear implant provided access to auditory perceptual information that was not previously available. Investigation into the speech production skills of these children postimplant is of interest because the speech of these young profoundly hearing-impaired children is in a constant state of development. METHOD: Phonetic inventories of nine children were monitored at preimplant and over the first 4 years of implant use using spontaneous speech samples collected at regular intervals for each child. Progress of phoneme acquisition was measured using two different criteria: targetless and target production. RESULTS: At 4 years postimplant, 87% of all phonemes had been acquired as targetless productions and 62% of all phonemes had been acquired as target productions. All monophthongs were acquired as target phonemes, but only 38% of the diphthongs and 54% of all consonants were acquired as targets over the time of the study. The average time taken for a phoneme to progress from targetless acquisition to target acquisition was 21.6 months, although variation among phonemes was evident. CONCLUSIONS: Overall, the data suggest similar trends in the order of phoneme acquisition when compared to normally-hearing children, although it would appear that the process of acquisition in children with cochlear implants occurs at a slower rate.