Introduction: Having an auditory pattern of behavior based on two ears is essential for sound localization, quality of hearing, understanding in groups, and with ambient noise. Aims and objectives: Describe and discuss: (1) The consequences of unilateral deafness. (2) The gradual recovery of failing neuronal circuits when stimulated with a cochlear implant. (3) The case of a blind patient with sudden unilateral deafness who required cochlear implantation that is used as a common thread for the subject. Materials and methods: Forty-five-year-old blind woman with sudden unilateral deafness. With unilateral deafness, she could not localize the sound source in terms of side nor if the sound came from above/below, near/far, or from front/back. Her hearing in groups and with ambient noise deteriorated. As a result, she lost her autonomy and required and underwent cochlear implantation. Results: It took her 2 years to recover full sound localization, to be able to discriminate in groups, and to recover binaural fusion. Recovery was gradual. Her abilities to localize sound source in terms of side, of being near or far, or coming from above or below recovered separately, that is to say, at different periods of time. Conclusion: After losing functional neuronal circuits, early stimulation with a cochlear implant helped to fully recover these circuits. Neuronal circuits for sound localization for side, coming from above or below, near or far are seemingly different since they recovered at different times. Hearing with both ears is essential for sound localization, discrimination in groups and with ambient noise.