We investigated the prevalence of hepatitis C virus (HCV) co-infection in HIV-infected patients at a large Swedish outpatient clinic. We also evaluated the feasibility of treating this patient group with pegylated-interferon alpha-2a and ribavirin (RBV) and found that only a small fraction of the HCV/HIV co-infected patients met the criteria for HCV treatment when following international guidelines. Thus, 11 patients were treated, and HCV kinetics were measured during early treatment. The overall treatment response rate was surprisingly high (73%) and correlated to early virological response.