Five Human Immunodeficiency Virus (HIV) seropositive homosexually active men experienced hepatitis C-seroconversion in the period between September 2004 and January 2007 at a single HIV Reference Center (University Hospital Ghent, Belgium). There was no history of intravenous drug use. All had unprotected anal sex with multiple other HIV seropositive men in the recent past. All of them had clinical syphilis and/or lymphogranuloma venereum rectitis within three to six months before the hepatitis C-seroconversion was detected. This confirms the observations in other case reports and studies originating from the Netherlands, France, the United Kingdom and Germany, illustrating sexual transmission of hepatitis C virus (HCV) infection in this high-risk group. Physicians should be aware of the persistent high-risk behaviour in a subgroup of HIV seropositive homosexually active men and perform intensive sexual counselling and screening for other sexually transmitted diseases, including HCV, during medical follow-up.