Neurofibromatosis type 2 (NF2) causes bilateral hearing loss due to tumour growth in the cerebellopontine angle. We report the results of promontory testing and transtympanic electrocochleography on subjects with deafness due to NF2 referred for an auditory brainstem implant. All 19 ears tested revealed loss of cochlear microphonics. Nine ears (mainly without previous treatment) revealed auditory perception during promontory stimulation, indicating cochlear deafness. One of these subjects has been successfully provided with a cochlear implant. The other 10 ears (mainly after previous surgery) revealed negative promontory stimulation, indicating additional retrocochlear deafness. These findings indicate that neurofibromas initially cause a cochlear deafness, so that a cochlear implant can be used if the auditory nerve can be preserved. This option has to be considered in rehabilitating patients with bilateral tumours due to NF2.