We estimate that only one-third of patients coinfected with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) are eligible for therapy for HCV with interferon (IFN) and ribavirin, and, of those who are eligible, two-thirds decline treatment. To date we have initiated treatment with IFN and ribavirin for 8% of coinfected patients evaluated, and <1% of patients have had a sustained virological response. During this process, we have identified many problems that significantly limit our ability to initiate and complete treatment with IFN in this population and have categorized these difficulties into 4 main challenges. They include access to care, contraindications or barriers to treatment, patients' reluctance to start treatment with IFN, and the low tolerability of treatment. If patients coinfected with HCV and HIV are to be treated for hepatitis C in greater numbers, these issues will need to be addressed.