목적: To investigate the changes of tinnitus in patients with profound sensorineural hearing loss after cochlear implantation (CI) in prospective, multicenter settings, and to find out clinical and audiologic factors related to these changes 방법:From August 2012 to December 2014, 81 adult patients underwent CI in 4 tertiary university hospitals, and 2 private clinics, were included in this study. We conducted same questionnaires for tinnitus 5 times in one patient before operation and immediately after operation, 1, 3, and 6 months after CI use. The questionnaires included visual analogue scale (VAS) of tinnitus severity, Tinnitus handicap index (THI), Becks depression index, and BEPSI (Brief Encounter Psychosocial Instrument). 결과:Among 81 patients, 59 patients had tinnitus before CI (72.8%). Before CI, the mean THI of the patients was high as 46.1, and all VAS were also high. These mean THI and VAS did not change immediately after CI, but 1 month after CI use, all the scores were significantly reduced, and the consecutive 4th and 5th tinnitus questionnaires also showed similar results with 3rd one. We investigated the factors related these tinnitus reduction, but the type of operations (round window approach VS cochleostomy), the depth of electrode insertion, hearing performance with CI, and threshold shift at low tone residual hearing did not show any relations. In CI off state, 8 patients of 34 patients who responded this question said their tinnitus suppressed steadily. Finally 5 patients among 22 patients who did not have tinnitus before CI, presented tinnitus after CI, but tinnitus of 4 patients was resolved during follow up period. 결론:CI in the patients with profound hearing loss, not only rehabilitates their hearing, but also reduces tinnitus. Because the most of tinnitus reduction occurred early period of CI use, we suggest masking or electric stimulation by CI was most important mechanism of tinnitus suppression by CI.