PURPOSE: Hereditary spherocytosis (HS) is the commonest cause of inherited hemolytic anemia in Korea. In hereditary spherocytosis patients, parvovirus B19 infection causes transient severe anemia, so called aplastic crisis. This study designed to characterize the clinical features and laboratory findings of hereditary spherocytosis patients with and without aplastic crisis, and define the serologic responses of parvovirus B19 infection in hereditary spherocytosis patients who presented with aplastic crisis. METHODS: We reviewed the medical records of the patients with hereditary spherocytosis visited at the Department of Pediatrics, Kyungpook National University Hospital, Daegu, Korea from June 1995 to Feburary 2006. Hereditary spherocytosis was diagnosed as anemia with reticulocytosis, indirect hyperbilirubinemia, spherocytosis, positive osmotic fragility test and splenomegaly. Aplastic crisis was defined as fever, abrupt onset of severe anemia and reticulocytopenia. And human parvovirus (HPV) B19 infection was proven by the presence of IgM antibodies to HPV B19 and/or the detection of virus DNA using the PCR technique. RESULTS: Thirteen cases were diagnosed as hereditary spherocytosis. Of the 13 patients, 6 were boys and 7 girls, the mean age at diagnosis was 3.9 years (range: 0.2~8.3 years), and the family history was positive in 10 cases (76.9%). One case was showed aplastic crisis as initial presentation and was confirmed as hereditary spherocytosis in the recovery phase. Another one case was diagnosed as hereditary spherocytosis at previous hospital. The mean follow up duration was 3.6 years (range: 0~8.5 years). The mean hemoglobin was 9.5 g/dL (range: 7.9~11.1 g/dL), the mean reticulocyte count was 11.9% (range: 6.0~25.4%), the mean reticulocyte index (RI) was 4.3 (range: 2.7~8.5) and the mean indirect bilirubin was 2.6 mg/dL (range: 1.0~6.6 mg/dL) at initial diagnosis as hereditary spherocytosis in 11 cases. Hepatomegaly appeared in 3 cases (27.3%) (mean size: 0.7+/-0.2 cm) and splenomegaly appeared in all cases (mean size: 2.0+/-0.4 cm). Osmotic fragility test was performed at 9 cases (69.2%) and all of them showed increased osmotic fragility compared with control (the mean NaCl concentration (%) was 0.62+/-0.03% at begin of hemolysis and 0.45+/-0.02% at complete of hemolysis). Aplastic crisis was seen in 9 patients (69.2%) at the mean age of 7.0 years (range: 5.3~10.8 years) and there was no second episode of aplastic crisis at same patient. In aplastic crisis patients, the mean hemoglobin was 4.3 g/dL (range: 2.8~6.8 g/dL), the mean reticulocyte count was 1.6% (range: 0.5~4.6%), the mean reticulocyte index (RI) was 0.2 (range: <0.1~0.8) and the mean indirect bilirubin was 2.1 mg/dL (range: 0.6~4.9 mg/dL). And liver size (mean: 2.9+/-0.7 cm) and spleen size (mean: 5.0+/-0.8 cm) were increased. HPV B19 IgM and/or HPV PCR were positive in all aplastic crisis patients. Splenectomy was performed in 7 cases (53.8%) at the mean age of 7.7 years (range: 6.3~10.2 years). CONCLUSION: There were 13 cases of hereditary spherocytosis and 9 cases of aplastic crisis due to parvovirus B19 infection. We have to inform the patients and their family about the importance of aplastic crisis with the abrupt onset of severe anemia.