Purpose: Targeted radiotherapy with 131iodine-metaiodobenzylguanidine (131I-MIBG) is effective for neuroblastoma (NBL), although optimal scheduling during high-risk (HR) treatment is being investigated. We aimed to evaluate the feasibility of stem cell apheresis and study hematologic reconstitution after autologous stem cell transplantation (ASCT) in patients with HR-NBL treated with upfront 131I-MIBG-therapy. Experimental Design: In two prospective multicenter cohort studies, newly diagnosed patients with HR-NBL were treated with two courses of 131I-MIBG-therapy, followed by an HR-induction protocol. Hematopoietic stem and progenitor cell (e.g., CD34þ cell) harvest yield, required number of apheresis sessions, and time to neutrophil (>0.5 109/L) and platelet (>20 109/L) reconstitution after ASCT were analyzed and compared with "chemotherapy-only"–treated patients. Moreover, harvested CD34þ cells were functionally (viability and clonogenic capacity) and phenotypically (CD33, CD41, and CD62L) tested before cryopreservation (n ¼ 44) and/or after thawing (n ¼ 19). Results: Thirty-eight patients (47%) were treated with 131I-MIBG-therapy, 43 (53%) only with chemotherapy. Median cumulative 131I-MIBG dose/kg was 0.81 GBq (22.1 mCi). Median CD34þ cell harvest yield and apheresis days were comparable in both groups. Post ASCT, neutrophil recovery was similar (11 days vs. 10 days), whereas platelet recovery was delayed in 131I-MIBG- compared with chemotherapy-only–treated patients (29 days vs. 15 days, P ¼ 0.037). Testing of harvested CD34þ cells revealed a reduced post-thaw viability in the 131I-MIBG-group. Moreover, the viable CD34þ population contained fewer cells expressing CD62L (L-selectin), a marker associated with rapid platelet recovery. Conclusions: Harvesting of CD34þ cells is feasible after 131I-MIBG. Platelet recovery after ASCT was delayed in 131I-MIBG-treated patients, possibly due to reinfusion of less viable and CD62L-expressing CD34þ cells, but without clinical complications. We provide evidence that peripheral stem cell apheresis is feasible after upfront 131I-MIBGtherapy in newly diagnosed patients with NBL. However, as the harvest of 131I-MIBG-treated patients contained lower viable CD34þ cell counts after thawing and platelet recovery after reinfusion was delayed, administration of 131I-MIBG after apheresis is preferred.