Background & Aims Dual chronic infection with hepatitis C virus (HCV) and hepatitis B virus (HBV) is common in areas endemic for either virus. Combination therapy with ribavirin and pegylated interferon (peginterferon) is the standard of care for patients with HCV monoinfection. We investigated the effects of combination therapy in patients infected with both HBV and HCV (genotypes 1, 2, or 3). Methods The study included 321 Taiwanese patients with active HCV infection; 161 also tested positive for hepatitis B surface antigen (HBsAg) and 160 were HBsAg-negative (controls). Patients with HCV genotype 1 infection received peginterferon alfa-2a (180 μg) weekly for 48 weeks and ribavirin (1000–1200 mg) daily. Patients with HCV genotypes 2 or 3 received peginterferon alfa-2a weekly for 24 weeks and ribavirin (800 mg) daily. At 24 weeks posttreatment, patient samples were examined for a sustained virologic response (SVR) against HCV (serum HCV levels decreased to <25 IU/mL). Results In patients with HCV genotype 1 infection, the SVR was 72.2% in dually infected patients vs 77.3% in monoinfected patients after treatment. For patients with HCV genotype 2/3 infections, the SVR values were 82.8% and 84.0%, respectively, after treatment. Serum HBV DNA eventually appeared in 36.3% of 77 dual-infected patients with undetectable pretreatment levels of HBV DNA; this was not accompanied by significant hepatitis. Posttreatment HBsAg clearance was observed in 11.2% of 161 dual-infected patients. Conclusions Combination therapy with peginterferon alfa-2a and ribavirin is equally effective in patients with HCV monoinfection and in those with dual chronic HCV/HBV infection.