Persistent pure red cell aplasia can be a manifestation of parvovirus B19 infection in immunocompromised hosts. Failure of the humoral immune response to clear parvovirus B19 in such patients results in persistent pure red cell aplasia. The authors describe a child who had T-cell immunodeficiency and persistent pure red cell aplasia due to parvovirus B19 infection. Interestingly, they detected human parvovirus B19 genome by polymerase chain reaction (PCR) not in the peripheral blood, but in the bone marrow specimen of the patient. In their patient, T-cell immunodeficiency may have caused impaired B-cell activation and failure of effective humoral immune response to neutralize the virus. Additionally, before the diagnosis of pure red cell aplasia, IVIG treatment given at a dosage of 400 mg/kg/day with 3-week intervals may result in sufficient neutralization of peripheral blood parvovirus B19, whereas it may not be sufficient for the neutralization of parvovirus B19 genome in bone marrow. Thus, peripheral blood parvovirus B19 serology (IgM and IgG) and PCR were negative, whereas bone marrow aspiration sample was positive for parvovirus B19 PCR in this patient. Reticulocytopenia and severe anemia may warn the physicians of parvovirus B19 infection, especially in immunocompromised children. Diagnosis may require demonstration of absence of late erythroid precursors in the bone marrow as well as serologic testing and detection of parvovirus B19 genome by PCR in the serum and/or bone marrow samples of the patient.