At Nagoya Medical Center, 10 patients co-infected with HIV and HCV received peginterferon α (PEG-IFNα) plus ribavirin therapy. Three of the cases were HCV genotype 1b, 2 cases were HCV 3b, and 1 case each were 2b, 2c, 3a, 4a and 6n. Nine patients received anti HIV therapy from the beginning. In 5 of these patients, anti HIV therapy was modified when PEG-IFNα plus ribavirin treatment was started. Of the above, 7 patients completed the protocol. No patients had severe adverse effects. Sustained virological response was achieved in 1 of 4 (25%) of the patients with genotypes 1 or 4, and in 5 of 6 (83%) of the patients with other genotypes. PEG-IFNα plus ribavirin therapy is considered a safe and efficacious treatment for patients co-infected with HIV and HCV.