Human parvovirus B19 causes erythema infectiosum (fifth disease) and aplastic crisis. In pregnancy, B19 may be transmitted on to the fetus resulting in hydrops fetalis. B19 is sometimes associated with thrombocytopenia and vasculitis. In immunocompromised patients, B19 may persist causing chronic infection. Several methods for detecting B19 virus or specific antibodies are now available. B19 infection does not usually require therapy. Efficacy of immunoglobulins in chronic B19 infection has been demonstrated.