Background and Objectives: Blood donor units are not screened for human parvovirus B19 (B19) even though it can be acquired via blood products. We estimated the prevalence of B19 in a US volunteer blood donor population and determined the clinical outcomes of transfusion recipients. Materials and Methods: Donor units were screened for B19 DNA by PCR, and positive units analyzed by EIA for B19 Ig. Unit usage was determined and recipient chart review conducted. Results: B19 DNA was detected in 11/9, 568 allogeneic units (0.1%), of which 3 had no measurable B19 Ig. One individual developed anemia consistent with B19 infection after receiving a DNA+ unit lacking B19 Ig. Conclusions: The apparent low incidence of disease in patients transfused with B19 DNA+ components may be due to coexistence of neutralizing antibodies in donors and/or recipients.