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123I-metaiodobenzylguanidine (MIBG) scans are preferable to 131I-MIBG for neuroblastoma imaging as they deliver less patient radiation yet have greater sensitivity in disease detection. Both 123I-MIBG and 131I-MIBG scans were used for disease assessments of neuroblastoma patients enrolled on Children's Oncology Group (COG) high-risk study A3973. The hypothesis was that 123I-MIBG and 131I-MIBG scans were sufficiently similar for clinical purposes in terms of ability to predict survival.Patients enrolled on COG A3973 with stage 4 disease who completed 123I-MIBG or 131I-MIBG scans at diagnosis, post-induction, post-transplant, or post-biotherapy were analyzed. The performance of the Curie score for each MIBG scan type in predicting survival was evaluated. At each time point, survival curves for 123I-MIBG versus 131I-MIBG were compared using the log-rank test.Of the 413 patients on A3973 with at least one MIBG scan, 350 were stage 4. The 5-year event-free survival (EFS) and overall survival (OS) rates were 33.4 ± 3.6% and 45.6 ± 4.0% (N = 350). At post-induction, EFS (P = 0.3501) and OS (P = 0.5337) for 123I-MIBG versus 131I-MIBG were not significantly different. Similarly, comparisons at the three other time points were non-significant.We found no evidence of a statistically significant difference in outcome by type of scan. For future survival analyses of MIBG Curie scores, 123I-MIBG and 131I-MIBG results may be combined and analyzed overall, without adjustment for scan type. Pediatr Blood Cancer 2011;56:1041–1045. © 2011 Wiley-Liss, Inc.