Although the number of studies using tandem high-dose chemotherapy and autologous stem cell transplantation (HDCT/autoSCT) for the treatment of high-risk pediatric solid tumors has been increasing, documentation of hematologic recovery after tandem HDCT/autoSCT is very limited. For this reason, we retrospectively analyzed the hematologic recovery of 236 children with high-risk solid tumors who underwent tandem HDCT/autoSCT. The median numbers of CD34(+) cells transplanted during the first and second HDCT/autoSCT were 4.3 × 10(6)/kg (range 0.6-220.2) and 4.1 × 10(6)/kg (range 0.9-157.6), respectively (P = 0.664). While there was no difference in neutrophil recovery between the first and second HDCT/autoSCT, platelet and RBC recoveries were significantly delayed in the second HDCT/autoSCT (P < 0.001 and P < 0.001, respectively). Delayed recovery in the second HDCT/autoSCT was more prominent when the number of transplanted CD34(+) cells was lower, especially if it was < 2 × 10(6)/kg. A lower CD34(+) cell count was also associated with increased RBC transfusion requirements and a higher serum ferritin level after tandem HDCT/autoSCT. More CD34(+) cells need to be transplanted during the second HDCT/autoSCT in order to achieve the same hematologic recovery as the first HDCT/autoSCT.