Deafblindness is a rare disease in which a person has a combination of hearing loss and vision loss, resulting in reduced access to both auditory and visual information. There are many reasons to occur of deafblindness: hereditary syndromes/disorders (CHARGE syndrome, Usher’s syndrome, Down’s syndrome), diseases that occurred before childbirth (cytomegalovirus, hydrocephalus, microcephaly), etc. The article presents a clinical case of an 11-year-old patient with a diagnosis of severe bilateral sensorineural hearing loss, condition after cochlear implantation on the right in 2012. Retinopathy of prematurity of the 5th degree, total retinal detachment with severe intraretinal proliferation. Infantile cerebral palsy. Hyperhomocysteinemia. Mitochondrial dysfunction. Casein intolerance. Persistent viral infection of Herpes Simplex Virus (HSV) type 6, Epstein–Barr virus (EBV). The authors showed a method for fitting the cochlear implant (CI) processor in a deaf-blind child by assessing the thresholds for perceiving sounds at different speech frequencies (500 Hz–4,000 Hz), which is the registration via Auditory Steady State Response (ASSR) to acoustic stimuli delivered through loudspeakers to an activated cochlear implant processor.