In cases of sudden deafness (SD), hearing recovery is generally assessed by classifying recovery into four degrees. To evaluate factors that may affect the prognosis for hearing recovery (e.g., hearing level at initial examination, days elapsed from onset of hearing loss to start of treatment) or drug efficacy, however, a quantitative method would be more advantageous. In the present study, therefore, the recovery rate was used as an index in investigating the prognosis and the efficacy of steroid treatments in 183 patients with SD first examined within 14 days after the onset of hearing loss during the period 1980-85. As with the degree of hearing recovery, the recovery rate was found to be favorable in those patients with good hearing at the initial examination, no vertigo, little difference in high-tone and low-tone hearing loss, and only a short lag between onset of symptoms and the initiation of treatment. This indicated that the recovery rate could be used as an index for the evaluation of hearing recovery in cases of sudden deafness. The efficacy of steroid treatment was evaluated in patients in whom the average of the hearing levels at five frequencies from 250 to 4,000 Hz was 40-90 dB. No significant differences were found in either recovery rate or degree of recovery between those patients who received steroids and those who did not. This was believed to be attributable to the variety of pathological conditions involved in SD and to the influence of the other, non-steroidal drugs administered.