Hepatitis B virus (HBV) and hepatitis C virus (HCV) coinfection is frequently associated with progressive liver disease. Treatment options are limited and no data on the efficacy of pegylated interferon (PEG-IFN) plus ribavirin therapy are available. We report a case of a 49-year-old woman with chronic hepatitis B and C who was scheduled for a 48 weeks course of PEG-IFNalpha-2b plus ribavirin therapy. She had HCV genotype 2 infection and was negative for HBV-DNA and HBe antigen before treatment. Although the HCV-RNA response was rapid until week 12, hepatitis B surface antigen (HBsAg) levels showed a more linear decline. At week 48, HBsAg was still positive, however, with very low levels of only 0.06 IU/ml. Treatment was therefore continued for another 4 weeks combined with active HBV immunization until HBs seroconversion occurred. Forty-three weeks after treatment, the patient showed a robust HBs seroconversion (anti-HBs of 260 IU/ml) and a sustained HCV-RNA response. This case highlights that combination therapy of PEG-IFNalpha-2b with ribavirin of HBV/HCV-coinfected individuals cannot only induce a sustained HCV-RNA response but also HBsAg seroconversion in single patients. Monitoring of HBsAg levels can be useful in individualizing optimal treatment duration in HBV-infected patients.