The B19 strain of parvovirus causes several distinct and important clinical diseases in humans. Aplastic crisis in patients with chronic hemolytic anemia, persistent bone marrow depression in immunocompromised individuals, and hydrops fetalis all result from direct infection of hematopoietic cells by the virus. Erythema infectiosum, arthritis, and purpuric vasculitis are postinfectious manifestations of B19 parvovirus infection.