In B‐cell malignancies, genes implicated in B‐cell differentiation, germinal center formation, apoptosis, and cell cycle regulation are juxtaposed to immunoglobulin loci through chromosomal translocations. In this study, we identified the BTB and CNC homology 2 (BACH2) gene as a novel translocation partner of the immunoglobulin heavy chain (IGH) locus in a patient with IGH‐MYC‐positive, highly aggressive B‐cell lymphoma/leukemia carrying der(14)t(8;14) and del(6)(q15). Fluorescence in situ hybridization analysis using an IGH/MYC probe detected an IGH‐MYC fusion signal on der(14) and IGH signal on del(6). Genome copy number analysis showed a deletion in the 6q15‐25 region and a centromeric breakpoint within the BACH2 gene. cDNA bubble polymerase chain reaction using BACH2 primers revealed that the first exon of Cδ was fused to the 5′‐untranslated region of BACH2 exon 2. The Cδ–BACH2 fusion transcript consisted of exon 1 of Cδ and exons 2 to 9 of BACH2, encompassing the entire BACH2 coding region, and the BACH2 was highly expressed in this patient. These results indicate that Cδ–BACH2 fusion may cause constitutive activation of BACH2. Although additional screening of 47 samples of B‐cell non‐Hodgkin's lymphoma (B‐NHL) patients and 29 cell lines derived from B‐cell malignancies by double‐color fluorescence in situ hybridization analysis detected a split signal with deletion of centromeric region of BACH2 only in a patient with follicular lymphoma, BACH2 was highly expressed in lymphoma cells of the patient and B‐NHL cell lines with IGH‐MYC translocation. These findings suggest that BACH2 plays a critical role in B‐cell lymphomagenesis, especially related to IGH‐MYC translocation in some way. © 2011 Wiley‐Liss, Inc.