Aim The fully implantable middle ear implant (C-FI-MEI) is designed for patients with moderate-to-severe sensorineural hearing loss or those with mixed hearing loss. To analyze the audiological post-operative results of subjects bilaterally implanted with C-FI-MEI. Materials and methods Retrospective study: 14 patients with bilateral, moderate-to-severe, sensorineural or mixed hearing loss were treated. This clinical sample included 14 cases bilaterally implanted (13 sequentially, 1 simultaneously). The evaluation at each follow-up after surgery included otologic examination, a structured interview, and different audiological tests composed of pure tone audiometry, speech in quiet and in noise test, and localization task. The mean follow-up was 67.2 +/- 33 months. Results There were no significant differences between pre and post-operative pure tone averages. The patients showed no significant differences between pre-operatively aided and C-FI-MEI implant-aided conditions in terms of word recognition score. Speech perception in noise under different loudspeaker arrangements and localization tests demonstrated a binaural advantage in bilaterally implanted patients. The mean daily use time was 17.4 and 16.7 h, respectively, for right and left side. Conclusion The results for the 14 patients, bilaterally implanted with C-FI-MEI, suggest that bilateral implantation of fully implantable middle ear hearing devices is an effective procedure.