Rarely, immunophenotypically immature B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) carries an immunoglobulin-MYC rearrangement (IG-MYC-r). This can result in diagnostic confusion with Burkitt lymphoma/leukaemia and use of unproven individualised treatment schedules. Here we contrast the molecular characteristics of these conditions and investigate historic clinical outcome data. We identified 90 cases registered on a national BCP-ALL clinical trial/registry. Where present, diagnostic material underwent cytogenetic, exome, methylome and transcriptome analysis. Outcome was analysed to define 3-year event free survival (EFS) and overall survival (OS). IG-MYC-r was identified in diverse cytogenetic backgrounds, co-existing with either: established BCP-ALL specific abnormalities (high hyperdiploidy n=3, KMT2A-rearrangement n=6, iAMP21 n=1, BCR-ABL n=1); BCL2/BCL6-rearrangements (n=15); or, most commonly, as the only defining feature (n=64). Within this final group, precursor-like V(D)J breakpoints predominated (8/9) and KRAS mutations were common (5/11). DNA methylation identified a cluster of V(D)J rearranged cases, clearly distinct from Burkitt leukaemia/lymphoma. Children with IG-MYC-r within that subgroup had 3-year EFS of 47% and OS of 60%, representing a high-risk BCP-ALL. To develop effective management strategies this patient group must be allowed access to contemporary, minimal residual disease adapted, prospective clinical trial protocols.