Previously, we reported the high prevalence of hepatitis C virus (HCV) infection in patients with oral cancer or oral lichen planus in Kyushu, Japan. We now report a 61-year-old man with chronic hepatitis C and no oral lesions who developed oral cancer 6 months after interferon therapy (interferon alpha [HLBI], 6 million units (MU) daily for 2 weeks and then 3 times a week for 14 weeks). This case emphasizes the need for periodic oral cavity examinations of hepatitis C patients and contributed to the investigation of oral cancer and HCV.