Parvovirus B19, the only known human pathogenic parvovirus, is associated with a wide range of disease manifestations. In healthy individuals, the major presentation of B19 infection is erythema infectiosum. In patients with underlying hemolytic disorders, infection is the primary cause of transient aplastic crisis. In immunosuppressed patients, persistent infection may develop that presents as pure red cell aplasia and chronic anemia. In utero infection may result in hydrops fetalis or congenital anemia. Diagnosis is based on examination of bone marrow and virologic studies. Much is known of the pathophysiology of the virus, and studies are in progress to develop a vaccine to prevent this widespread infection.