A 79-year-old woman complained of right hearing loss, tinnitus and dizziness. CT, MRI and angiography demonstrated a large aneurysm of the right vertebral artery. On the pure-tone audiogram, there was a remarkable difference between the right and left ears. On the left side hearing was almost normal for her age, although on the right side hearing at the frequency above the 1kHz was severely affected. Electrocochleography was performed using the extratympanic approach. The detection thresholds of both cochlear microphonics and action potential were lower than the audiometric threshold. In spite of the difference in the audiometric threshold between the right and the left ears, the DP audiograms were similar. The auditory brainstem response was normal in the left ear, but only wave I was demonstrated in the right ear. It is thought that these neurotological examinations showed retrocochlear hearing loss.