Parvovirus B19 (РВ19) is an ubiquitous single strand DNA-virus, which in healthy persons causes the so-called fifth disease -benign infectious exanthema. However, in patients with disturbed erythropoiesis or immune deficiencies PB19 infection can lead to potentially life-threatening syndromes. Three pediatric patients (females) with primary PB19 infection are described. One patient with hereditary spherocytosis developed a classical transitory aplastic crisis which required several blood transfusions. In a second patient with acquired aplastic anemia and high titers of PB19 in peripheral blood, long-lasting fewer, and rash hematopoietic stem cell transplantation had to be postponed for 2 weeks because of the risk of graft function suppression. In a third patient high titers of PB19 in bone marrow resulted in long-lasting aplasia and delay of scheduled intensive chemotherapy and hence, in relapse of underlying acute myeloid leukemia. Importantly that 2 of 3 patients (the second and the third one) received platelet transfusions from the same donor. So far, the problem of diagnosis, treatment and prevention of PB19 infection in patients with hematological/oncological diseases remains unresolved and needs further discussion.