Previous studies tried to correlate prognosis and response to oral corticosteroids in patients with idiopathic sudden sensorineural hearing loss to such factors as the age of the patient, presence of vertigo, shape of the audiogram, or severity of the hearing loss. However, temporal bone histopathologic evidence shows that idiopathic sudden sensorineural hearing loss may be caused by cochleitis or cochlear nerve neuritis. Herein we report results of a retrospective study of 96 consecutive patients with idiopathic sudden sensorineural hearing loss who were evaluated with auditory brain stem responses and gadolinium-enhanced magnetic resonance imaging. Results of the auditory brain stem response and magnetic resonance imaging were correlated with hearing outcome. Follow-up was available for 65 patients: 14 with abnormal and 51 with normal auditory brain stem responses. The overall rate of hearing recovery or improvement was 65% in the normal auditory brain stem response group compared with 43% in the abnormal auditory brain stem response group (p = 0.07). Among the 38 patients treated with a tapering course of oral corticosteroids, the recovery or improvement rate was 83% for those with normal auditory brain stem responses and 56% for those with abnormal auditory brain stem responses (p < 0.05). Of the 27 patients who did not receive steroid therapy, the improvement rate was 41% in those with normal auditory brain stem responses and 20% in those with abnormal auditory brain stem responses (p = 0.09). Magnetic resonance imaging with gadolinium was obtained on all 14 patients with abnormal auditory brain stem responses but on none with normal auditory brain stem responses.(ABSTRACT TRUNCATED AT 250 WORDS)