Combination therapy of pegylated interferon alpha and ribavirin has been associated with various adverse effects, but sudden-onset hearing loss is uncommon. We report a 60-year-old male patient who developed sudden-onset hearing loss during combination therapy with pegylated interferon alpha and ribavirin for chronic hepatitis C. This patient had been diagnosed with chronic hepatitis C (genotype Ib) and early-stage liver cirrhosis 3 years previously, and had been treated with conventional interferon-alpha and ribavirin for 12 months. However, 6 months from the end of the treatment course the patient relapsed and received combination retreatment with pegylated interferon alpha-2b and ribavirin. He developed sudden-onset right-side hearing loss and tinnitus 42 weeks after the start of this retreatment. Pure-tone audiometry revealed a right-side hearing loss of 60 approximately 90 dB. The patient consequently immediately discontinued the pegylated interferon therapy and was given prednisone 60 mg/day for 10 days, after which the hearing loss had almost completely recovered.