BACKGROUND/AIM: Idiopathic sudden sensorineural hearing loss (ISSHL) is one of the most controversial issues in otology. The aim of this study was to determine whether a delay in treatment has any influence on hearing recovery in ISSHL. METHOD: This study was designed as a retrospective evaluation of an electronic patient data base of the University Hospital Zürich from January 1995 to August 2006. Five hundred and forty one patients with a sudden hearing loss were identified. The standard treatment was carbogen inhalation (95% O2 and 5% CO2 eight times per day in the duration of 30 minutes) and prednisone orally (100 mg in one morning dose) for 7 days. Factor that was analyzed included the interval between the onset of symptoms and the beginning of the treatment. The initial hearing loss was described using the pure tone average (PTA in dB) heating level at 4 frequencies (0.5, 1, 2 and 4 kHz). Hearing gain was expressed either as absolute hearing gain (dB values from initial PTA minus dB values from final PTA) or as relative hearing gain (absolute hearing gain divided by initial PTA minus baseline PTA) x 100. Significant recovery of heating was defined as the final PTA < or =30 dB (or same as PTA of the opposite ear). RESULTS: An absolute hearing gain between the initial audiogram and the final audiogram was 15.1 dB. The mean relative heating gain was 47%. Three hundred one (57%) patients had a significant recovery of hearing, and 228 (43%) had not. If the patients received treatment in the first 24 hours after onset of symptoms, then the rate of significant recovery was 56%, and no significant difference existed between this group and the patients who received the therapy after 24 hours, but within seven days (chi2=0.007, DF=1, p>0.01). CONCLUSION: These results suggest that it is not critical to begin the treatment of ISSHL immediately as an emergency, but within seven days.