Hepatitis C (HCV) contributes significantly to the morbidity and mortality of patients coinfected with human immunodeficiency virus (HIV) and those with recurrent hepatitis C after successful liver transplantation. Treatment of hepatitis C in these patient populations, while crucial, can be quite challenging. Baseline cytopenias, in particular, may limit dosing of interferon and/or ribavirin or preclude therapy entirely when standard guidelines are followed. Concomitant medications, opportunistic infections, and other bone marrow insults account for the anemia, neutropenia, and thrombocytopenia frequently encountered in these patients. Sustained virologic response rates in published series for HIV/HCV and post-transplantation HCV have not reached those seen in treatment of HCV alone, despite the highly selected patient populations chosen for these studies. Hematopoietic growth factors such as erythropoietin and granulocyte-colony stimulating factors may be used to improve the anemia and neutropenia seen during treatment of HCV. Reported experience with these growth factors is limited in HIV/HCV coinfected patients, but studies are underway to determine if growth factors improve adherence to therapy and perhaps virologic response rates. Post-transplantation studies of HCV therapy have reported more liberal use of growth factors; however, discontinuation rates have been high and virologic response rates have been disappointing. Further study of growth factors as a means to increase sustained virologic response rates and maintain adequate dosing and duration of interferon and ribavirin therapy in these patient populations is needed.