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Background Aims: Peripheral blood stem cells (PBSC) are increasingly used as an alternative to bone marrow in autologous transplantations. In adult patients, the peripheral blood CD34(+) cell count is a good predictor of CD34(+) cell yield in apheresis. However, the determinants of stem cell yield in the pediatric population have not been well established., Methods: We retrospectively studied 396 apheresis procedures in 301 pediatric patients. Receiver operating characteristic (ROC) curves based on pre-apheresis peripheral blood CD34(+) cell counts were generated to facilitate prediction of the optimal timing of PBSC collection. The associations between CD34(+) cell yield and age and mobilization regimen were analyzed., Results: Significant differences in CD34(+) cell yield among different age groups were observed. Furthermore, higher CD34(+) cell yields were obtained in patients receiving chemotherapy as part of the mobilization regimen than those without chemotherapy. A correlation was noted between the CD34(+) cell yield and blood surrogate markers, including white blood cell count, absolute neutrophil count and pre-apheresis peripheral blood CD34(+) cell count. Cut-off values of > 35 CD34(+) cells/μL in patients < 15 years old and > 45 CD34(+) cells/μL in patients ≥ 15 years old were strong predictors of an adequate PBSC collection in one apheresis session. For clinical use, ROC curves and tables were generated to assist advance planning for PBSC collection., Conclusions: The pre-apheresis peripheral blood CD34(+) cell count is most useful in predicting PBSC yield. Our new cut-off values have better operating characteristics for children than the conventional value of 20 CD34(+) cells/μL used for adults.