Patients coinfected with both hepatitis C virus (HCV) and the human immunodeficiency virus (HIV) have more rapid progression of HCV infection; however, little is known about the effect of coinfection with HCV on the progression of HIV disease. This study assessed the association between infection with different HCV genotypes on progression to AIDS and death in a cohort of men with hemophilia. Patients infected with HCV type 1 experienced a more rapid progression to both AIDS (P = .009) and death (P = .007) than did those infected with other types. This effect was largely independent of age at seroconversion, hemophilia diagnosis, and changes in CD4 cell count over the follow-up period. These results suggest an association between HCV genotype and progression of HIV disease, which, if confirmed, could have important implications for the treatment and care of patients coinfected with both HIV and HCV.