Older adults with hearing impairment have a higher risk for accelerated cognitive decline compared to normal-hearing individuals. The aim of this study was to evaluate the long-term effect of cochlear implantation on cognition and Health-Related Quality of Life (HRQoL) in older adults with severe-to-profound hearing loss. All included subjects were 55 years or older with postlingual, bilateral, severe-to-profound hearing loss, and received a unilateral cochlear implant (CI). Cognition was evaluated using the Repeatable Battery for the Assessment of Neuropsychological Status for Hearing Impaired Individuals (RBANS-H), and HRQoL was evaluated using the following five questionnaires; Nijmegen Cochlear Implant Questionnaire (NCIQ); Hearing Implant Sound Quality Index (HISQUI); Speech, Spatial, and Qualities of Hearing Scale (SSQ12); Hospital Anxiety and Depression scale (HADS); and Type D questionnaire (DS14). Individuals were evaluated preoperatively, and annually up to four years after CI activation. One year after cochlear implantation a significant improvement was observed in the total RBANS-H score (p<0.001) and the subdomain scores “Immediate Memory” (p=0.005), “Attention” (p=0.048), and “Delayed memory” (p=0.017). When comparing preoperative results with four years postoperative results, a significant improvement was observed in “Immediate Memory” (p=0.020) and a significant decline was observed in “Visuospatial Memory” (p=0.013). Four years after implantation, no significant improvement was observed in the total RBANS-H score. A significant improvement was observed for the HRQoL questionnaires one year after cochlear implantation. To conclude, unilateral cochlear implantation in an adult population with bilateral severe-to-profound SNHL has a positive effect on cognitive functioning and HRQoL one year after activation.