Human parvovirus B19 is the infectious agent of erythema infectiosum, a mild exanthematous illness common in children. In certain vulnerable subjects, it causes life-threatening illness including transient aplastic anemia and chronic bone marrow failure. Fatal myocarditis has also been reported, and it is known to cause intrauterine infection that can result in fetal death. This review briefly outlines the increasing range of illnesses produced by parvovirus B19 in children, neonates, and the fetus. Particular attention is paid to the risk that maternal infection with parvovirus B19 poses to the unborn child, because the quantitation of this risk has been a major recent contribution. Recent advances in our knowledge of its epidemiology, transmission, laboratory diagnosis, and treatment are presented.