The purpose of the present study was to compare the growth function of pre-first word vocalizations of infants with normal hearing (NH) to that of hearing-impaired (HI) infants pre- and post-cochlear implantation. Subjects included 163 infants between 0.5 and 20 months old with normal hearing and known normal development, and, 18 infants with cochlear implants (CI) who were implanted between 11 and 29 months. Pre-first word vocalization was assessed using the PRoduction Infant Scale Evaluation (PRISE) test. Parents of infants were interviewed using 11 probes reflecting known milestones in the infant's vocal development that lead to the first-word stage. NH infants show an exponential growth function of vocal development, which plateaus at approximately 13 months. HI infants show limited vocalizations before implantation regardless of age. After cochlear implant, PRISE scores of CI are in keeping with normal development of pre-first word vocalizations when plotted as a function of duration of implant use. The PRISE test contributes to evaluating the effectiveness of the habilitation process in general, and the efficacy of the implant device in particular. It can also alert to production problems not related to hearing loss thus allowing for early intervention.