Background and Objectives: Human parvovirus B19 is a potential risk to hemophiliac patients receiving blood products. Materials and Methods: To determine the prevalence of the corresponding antibody in patients with hemophilia A or B or von Willebrand’s disease, we tested 326 hemophilia patients for anti-B19 IgG. The results were compared with those of 203 age-matched controls (male blood donors and children). Results: The overall prevalence of B19 IgG in the hemophilia patients was 302/326, and in the controls 123/203. Below the age of 10, hemophilia patients had a higher prevalence of B19 IgG (76%, 42/55) than the controls (23%, 11/48; p < 0.00001). In those below the age of 5 who had been treated exclusively with monoclonally purified concentrate, it made no difference whether the product was pasteurized or solvent-detergent treated. There was a significantly lower incidence in patients who were rarely treated. Conclusion: Parvovirus B19 is frequently transmitted in blood products. Existing virus-inactivating methods do not prevent transmission.