Electric acoustic stimulation (EAS) is the use of a hearing aid and a cochlear implant technology together in the same ear. EAS is intended for people with high-frequency hearing loss, who can hear low-pitched sounds but not high-pitched ones. The hearing aid acoustically amplifies low-frequency sounds, while the cochlear implant electrically stimulates the middle- and high-frequency sounds. The inner ear then processes the acoustic and electric stimuli simultaneously, to give the patient the perception of sound. In several clinical studies, EAS has proven to yield superior results compared to partially deaf patients who use only hearing aids. In order to achieve these results, it is vital to preserve the patient's residual hearing in the low frequencies. Introduction Electric stimulation of the auditory system via cochlear implant is a commonly used technique for individuals with a severe to profound sensorineural hearing loss, as well as for those adults and children with some residual hearing. Individuals with mild to moderate hearing loss can usually benefit from hearing aids. This acoustic stimulation proves to be particularly effective in the low frequencies, though a severe hearing loss (> 70 dB HL) above 1 kHz can be beyond the range of amplification possible via acoustic stimulation. Electric stimulation (CI), on the other hand, is capable of providing high-frequency information up to 8 kHz. The concept of combining simultaneous electric-acoustic stimulation (EAS) for the purposes of better hearing was first described by C. von Ilberg and J. Kiefer, from the Universitätsklinik Frankfurt, Germany, in 1999. That same year the first EAS patient was implanted. Indications There is a certain patient group that has some degree of residual hearing in the low frequencies and a severe hearing loss in the high frequencies. This group only receives limited benefits from traditional amplification because of the severity of the hearing loss in the high frequencies. They have inadequate speech comprehension, even in the best aided condition. Nor are they classic cochlear implant candidates, because of their mostly intact low frequency residual hearing. The indications for EAS are based on the following three considerations: Audiogram Speech scores Additional selection criteria Audiogram below 1.5 kHz – No or moderate HL above 1.5 kHz – Severe to profound sensorineural hearing impairment Speech scores The patient's monosyllable word score should be ≤ 60% at 65 dB SPL in the best aided condition. Additional selection criteria Contraindicated are: Progressive hearing loss. Autoimmune disease. Hearing