In the United States, approximately 30% of all human immunodeficiency virus (HIV)-positive patients are also infected with hepatitis C virus (HCV). Both viruses share similar routes of transmission. Unlike HIV or hepatitis B virus, HCV is curable if treated and the patient achieves a sustained virologic response. The impact of coinfection includes greater morbidity and mortality, with higher rates of opportunistic disease, development of cirrhosis, and death. The standard of treatment for HIV-HCV coinfection is similar to that for HCV monoinfection and consists of pegylated interferon alpha and ribavirin. As with HCV monoinfection, the best predictor of response to therapy for HIV-HCV coinfection is infection with an HCV genotype other than genotype 1 or 4. Adherence to treatment is critical for improving response to HCV therapy. However, considerable toxicities are associated with pegylated interferon alpha and ribavirin and pose particular problems in the coinfected patient. Coinfected patients are more likely to experience significant weight loss with HCV therapy. Neutropenia and anemia are both common laboratory abnormalities that necessitate dosage reductions and are concerns for development of acquired immunodeficiency syndrome-defining events. The effect of CD4(+) cell count has been evaluated both as a factor in response to HCV therapy and in stratification of risk for infection. Immunosuppression is not a contraindication to HCV therapy, although CD4(+) counts above 350 cells/mm(3) are associated with increased response rates in patients with HCV genotype 1 coinfection. Antiretroviral therapy does need to be adjusted to minimize adverse effects. Concomitant use of zidovudine is contraindicated because of its profound exacerbation of bone marrow suppression. The use of didanosine is also not indicated during HCV therapy because of the risks of hepatic decompensation. Controversy exists regarding the use of abacavir. Newer agents for HCV include the protease inhibitors telaprevir and boceprevir. Although results with the protease inhibitors are highly encouraging, their effects in coinfected patients have not been evaluated. Treatment for HCV in patients with HIV poses potential obstacles to success, but the benefits of viral eradication warrant the challenge of therapy.