Intraoperative monitoring of the auditory pathway by means of either electrocochleography or auditory brainstem response audiometry is valuable during hearing preservation vestibular schwannoma (VS) surgery. A more than 75% intraoperative reduction of the amplitude of these evoked auditory potentials was thought to be related with clear hearing compromise of hearing. We identified 22 patients who satisfied this intraoperative criterion in a cohort of 86 consecutive patients who had attempted hearing preservation VS surgery. The surgical step that temporally coincided with the above event was considered to be the most critical step for hearing monitoring during this kind of surgery. Most frequently, drilling of the internal auditory canal and direct tumor resection were associated with the aforementioned changes, but also drilling of the cortical temporal bone at the very beginning of surgery or the opening of the dura could be implicated. This profound intraoperative amplitude decrease was associated with a profound postoperative hearing impairment in 84% of the cases.