Sexual contact is thought to be an inefficient mode of hepatitis C virus (HCV) transmission. However, reports of sexually transmitted HCV infection among HIV-infected men who have sex with men (MSM) began to appear in 2004. The patients were of early middle age with well-controlled HIV infection, participated in unprotected receptive sex, and frequently used noninjection recreational drugs. Molecular studies showed evidence of clusters of transmission between patients in different countries in Europe. Spontaneous clearance was relatively rare, but treatment with pegylated interferon and ribavirin resulted in cure in about two thirds of patients. Of concern was the finding of moderately advanced fibrosis during the early stages of HCV infection. HIV-infected MSM are a new risk group for HCV infection and so should be screened regularly for HCV infection.