Older adults with a severe to profound hearing loss are more at risk of cognitive decline than adults of a similar age with milder losses or normal hearing. This poses challenges, not only in the assessment process, but also for rehabilitation of the hearing loss with a cochlear implant. Given that the patient’s hearing is likely to significantly improve with an implant, does giving an implant stop, reverse or have no effect on the cognitive declines these patients may be experiencing? These authors aim to investigate this point with a systematic review of the literature. Of the 2716 records retrieved during the search, only six articles (involving 166 patients) were found to directly compare cognition before and after cochlear implantation. Five out of the six studies showed an improvement in cognition after implantation. However, due to the nature of the studies, there was significant bias found that compounded the results, including suitability of cognitive tests, lack of a control group, the effect of improved hearing when administering the test material, and poor design and statistical analysis. All of the six studies suffer from at least one bias. This and the ageing population therefore highlight the need for a well-designed large-scale study to examine this question in more detail.