Background: Hearing loss may affect many aspects of a person's life. The age of cochlear implantation (CI) is often considered an important predictor of language skills of children with CI, but little is known about the benefits of early CI on speech intelligibility development in these children. This study aimed to compare language skills as well as intelligibility of speech in prelingual deaf patients who received CI before the age of six years and those who received CI after the age of six years with an 8-year follow-up.

Materials and Methods: This 8-year longitudinal, retrospective case–control study was conducted in 2021 at a cochlear implant center in Tehran, Iran. Thirty-one patients were included in two groups: late cochlear implant (n = 15), and early cochlear implant (n =16). The Test of Language Development- Primary (TOLD-P3) was used to assess the participants 'language skills. The intelligibility of the participants' speech was assessed through the Persian version of the Intelligibility Context Scale (ICS) and the speech intelligibility rating (SIR).

Results: These two groups did not show a significantly difference in terms of the language scores (P>0.05) but had a significantly difference in terms of the SIR and the ICS scores (P<0.05). Speech intelligibility had a significantly negative correlation with the age of CI (P<0.001), and had a significant positive correlation with language skills (P<0.001).

Conclusion: The long-term outcomes of early and late CI were similar in terms of the development of language skills but too different in terms of the intelligibility of speech. The age of CI had no effect on the language development but had a significant effect on speech intelligibility.